Publications by authors named "Rose Amal"

140 Publications

Manipulating the Fate of Charge Carriers with Tungsten Concentration: Enhancing Photoelectrochemical Water Oxidation of Bi WO.

Small 2021 Jul 28:e2102023. Epub 2021 Jul 28.

School of Energy and Environment, City University of Hong Kong, Kowloon, Hong Kong SAR, P. R. China.

Bismuth tungstate (Bi WO ) thin film photoanode has exhibited an excellent photoelectrochemical (PEC) performance when the tungsten (W) concentration is increased during the fabrication. Plate-like Bi WO thin film with distinct particle sizes and surface area of different exposed facets are successfully prepared via hydrothermal reaction. The smaller particle size in conjunction with higher exposure extent of electron-dominated {010} crystal facet leads to a shorter electron transport pathway to the bulk surface, assuring a lower charge transfer resistance and thus minimal energy loss. In addition, it is proposed based on the results from conductive atomic force microscopy that higher W concentration plays a crucial role in facilitating the charge transport of the thin film. The "self-doped" of W in Bi WO will lead to the higher carrier density and improved conductivity. Thus, the variation in the W concentration during a synthesis can be served as a promising strategy for future W based photoanode design to achieve high photoactivity in water splitting application.
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http://dx.doi.org/10.1002/smll.202102023DOI Listing
July 2021

Intrinsic ORR Activity Enhancement of Pt Atomic Sites by Engineering d-Band Center via Local Coordination Tuning.

Angew Chem Int Ed Engl 2021 Jul 26. Epub 2021 Jul 26.

University of New South Wales - Kensington Campus: University of New South Wales, School of Chemical Engineering, 2052, Sydney, AUSTRALIA.

A considerable amount of platinum (Pt) is required to ensure an adequate rate for oxygen reduction reactions (ORR) in fuel cells and metal-air batteries. Thus, the implementation of atomic Pt catalysts holds promise for minimizing the contents of Pt. In this contribution, atomic Pt sites with nitrogen (N) and phosphorus (P) co-coordination on carbon matrix (PtNPC) are conceptually predicted and experimentally developed to alter the d -band center of Pt, thereby promoting the intrinsic ORR activity. The PtNPC with a record-low Pt content (~0.026 wt%) consequently shows a benchmark-comparable activity for ORR with an onset of 1.0 V RHE and half-wave potential of 0.85 V RHE . It also features a high stability in 15,000-cycle tests and a superior turnover frequency of 6.80 s -1 at 0.9 V RHE . Damjanovic kinetics analysis reveals a tuned ORR kinetics of PtNPC from mixed 2/4-electron to predominate 4-electron route. It is discovered that coordinated P species significantly shifts d -band center of Pt atoms, accounting for the exceptional performance of PtNPC.
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http://dx.doi.org/10.1002/anie.202107790DOI Listing
July 2021

Designing Undercoordinated Ni-N and Fe-N on Holey Graphene for Electrochemical CO Conversion to Syngas.

ACS Nano 2021 Jul 1. Epub 2021 Jul 1.

School of Chemical Engineering, UNSW Sydney, Sydney, NSW 2052, Australia.

In this study, we propose a top-down approach for the controlled preparation of undercoordinated Ni-N (Ni-hG) and Fe-N (Fe-hG) catalysts within a holey graphene framework, for the electrochemical CO reduction reaction (CORR) to synthesis gas (syngas). Through the heat treatment of commercial-grade nitrogen-doped graphene, we prepared a defective holey graphene, which was then used as a platform to incorporate undercoordinated single atoms carbon defect restoration, confirmed by a range of characterization techniques. We reveal that these Ni-hG and Fe-hG catalysts can be combined in any proportion to produce a desired syngas ratio (1-10) across a wide potential range (-0.6 to -1.1 V vs RHE), required commercially for the Fischer-Tropsch (F-T) synthesis of liquid fuels and chemicals. These findings are in agreement with our density functional theory calculations, which reveal that CO selectivity increases with a reduction in N coordination with Ni, while unsaturated Fe-N sites favor the hydrogen evolution reaction (HER). The potential of these catalysts for scale up is further demonstrated by the unchanged selectivity at elevated temperature and stability in a high-throughput gas diffusion electrolyzer, displaying a high-mass-normalized activity of 275 mA mg at a cell voltage of 2.5 V. Our results provide valuable insights into the implementation of a simple top-down approach for fabricating active undercoordinated single atom catalysts for decarbonized syngas generation.
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http://dx.doi.org/10.1021/acsnano.1c03293DOI Listing
July 2021

Accelerating Electron-Transfer and Tuning Product Selectivity Through Surficial Vacancy Engineering on CZTS/CdS for Photoelectrochemical CO Reduction.

Small 2021 Jun 25:e2100496. Epub 2021 Jun 25.

School of Chemical Engineering, UNSW Sydney, Sydney, NSW, 2052, Australia.

Copper-based chalcogenides have been considered as potential photocathode materials for photoelectrochemical (PEC) CO reduction due to their excellent photovoltaic performance and favorable conduction band alignment with the CO reduction potential. However, they suffer from low PEC efficiency due to the sluggish charge transfer kinetics and poor selectivity, resulting from random CO reduction reaction pathways. Herein, a facile heat treatment (HT) of a Cu ZnSnS (CZTS)/CdS photocathode is demonstrated to enable significant improvement in the photocurrent density (-0.75 mA cm at -0.6 V vs RHE), tripling that of pristine CZTS, as a result of the enhanced charge transfer and promoted band alignment originating from the elemental inter-diffusion at the CZTS/CdS interface. In addition, rationally regulated CO reduction selectivity toward CO or alcohols can be obtained by tailoring the surficial sulfur vacancies by HT in different atmospheres (air and nitrogen). Sulfur vacancies replenished by O-doping is shown to favor CO adsorption and the CC coupling pathway, and thereby produce methanol and ethanol, whilst the CdS surface with more S vacancies promotes CO desorption capability with higher selectivity toward CO. The strategy in this work rationalizes the interface charge transfer optimization and surface vacancy engineering simultaneously, providing a new insight into PEC CO reduction photocathode design.
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http://dx.doi.org/10.1002/smll.202100496DOI Listing
June 2021

Designing optimal integrated electricity supply configurations for renewable hydrogen generation in Australia.

iScience 2021 Jun 15;24(6):102539. Epub 2021 May 15.

Collaboration on Energy and Environmental Markets, The University of New South Wales, Sydney, NSW 2052, Australia.

The high variability and intermittency of wind and solar farms raise questions of how to operate electrolyzers reliably, economically, and sustainably using predominantly or exclusively variable renewables. To address these questions, we develop a comprehensive cost framework that extends to include factors such as performance degradation, efficiency, financing rates, and indirect costs to assess the economics of 10 MW scale alkaline and proton-exchange membrane electrolyzers to generate hydrogen. Our scenario analysis explores a range of operational configurations, considering (i) current and projected wholesale electricity market data from the Australian National Electricity Market, (ii) existing solar/wind farm generation curves, and (iii) electrolyzer capital costs/performance to determine costs of H production in the near (2020-2040) and long term (2030-2050). Furthermore, we analyze dedicated off-grid integrated electrolyzer plants as an alternate operating scenario, suggesting oversizing renewable nameplate capacity with respect to the electrolyzer to enhance operational capacity factors and achieving more economical electrolyzer operation.
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http://dx.doi.org/10.1016/j.isci.2021.102539DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8184509PMC
June 2021

Liquid Crystal-Mediated 3D Printing Process to Fabricate Nano-Ordered Layered Structures.

ACS Appl Mater Interfaces 2021 Jun 10;13(24):28627-28638. Epub 2021 Jun 10.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney 2052, New South Wales, Australia.

The emergence of three-dimensional (3D) printing promises a disruption in the design and on-demand fabrication of smart structures in applications ranging from functional devices to human organs. However, the scale at which 3D printing excels is within macro- and microlevels and principally lacks the spatial ordering of building blocks at nanolevels, which is vital for most multifunctional devices. Herein, we employ liquid crystal (LC) inks to bridge the gap between the nano- and microscales in a single-step 3D printing. The LC ink is prepared from mixtures of LCs of nanocellulose whiskers and large sheets of graphene oxide, which offers a highly ordered laminar organization not inherently present in the source materials. LC-mediated 3D printing imparts the fine-tuning required for the design freedom of architecturally layered systems at the nanoscale with intricate patterns within the 3D-printed constructs. This approach empowered the development of a high-performance humidity sensor composed of self-assembled lamellar organization of NC whiskers. We observed that the NC whiskers that are flat and parallel to each other in the laminar organization allow facile mass transport through the structure, demonstrating a significant improvement in the sensor performance. This work exemplifies how LC ink, implemented in a 3D printing process, can unlock the potential of individual constituents to allow macroscopic printing architectures with nanoscopic arrangements.
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http://dx.doi.org/10.1021/acsami.1c05025DOI Listing
June 2021

Oxygen Nucleation of MoS Nanosheet Thin Film Supercapacitor Electrodes for Enhanced Electrochemical Energy Storage.

ChemSusChem 2021 Jul 14;14(14):2882-2891. Epub 2021 Jun 14.

School of Chemical Engineering, The University of New South Wales, Sydney, NSW, 2052, Australia.

A direct thin film approach to fabricate large-surface MoS nanosheet thin film supercapacitors using the solution-based diffusion of thiourea into an anodized MoO thin film was investigated. A dense MoS nanosheet thin film electrode (D-MoS ) was obtained when the anodized MoO thin film was processed in a low thiourea solution concentration, whereas a highly porous MoS nanosheet thin film electrode (P-MoS ) was formed at a higher thiourea solution concentration. The charge storage performances of the D-MoS and P-MoS thin films displayed an unusual increase in capacitance on extended cycling, leading to a capacitance as high as around 5-8 mF cm . X-ray diffraction and cross-sectional microscopy revealed the capacitance enhancements of the MoS supercapacitors are attributable to the nucleation of a new MoS O phase upon cycling. For the D-MoS nanosheet thin film, the formation and growth of the MoS O phase during cycling was accompanied by a volumetric expansion of the MoS layer. For the P-MoS thin film, the nucleation and growth of the MoS O phase occurred in the pores of the MoS layer. The propagation of the MoS O phase also shifted the charge storage process in both films from a diffusion-limited process to a capacitive-dominant process.
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http://dx.doi.org/10.1002/cssc.202100941DOI Listing
July 2021

Ligand-Promoted Cooperative Electrochemical Oxidation of Bio-Alcohol on Distorted Cobalt Hydroxides for Bio-Hydrogen Extraction.

ChemSusChem 2021 Jun 13;14(12):2612-2620. Epub 2021 May 13.

School of Chemical Engineering, The University of New South Wales, Sydney, NSW, 2052, Australia.

Hydrogen is increasingly viewed as a game-changer in the clean energy sector. Renewable hydrogen production from water is industrialized by integrating water electrolysis and renewable electricity, but the current cost of water-born hydrogen remains high though. An ideal scenario would be to produce value-added chemicals along with hydrogen so the cost can be partially offset. Herein, facilitated bio-hydrogen extraction and biomass-derived chemical formation from sugar-derived 5-hydroxymethyfurfural (HMF) were achieved via the in-situ transformation of cobalt-bound electrocatalysts. The cyanide-bound cobalt hydroxide exhibited a low voltage at 1.55 V at 10 mA cm for bio-hydrogen production, compared with an iridium catalyst (1.75 V). The interaction between the biomass intermediate and the cyanide ligand is suggested to be responsible for the improved activity.
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http://dx.doi.org/10.1002/cssc.202100722DOI Listing
June 2021

Microstructural Engineering of Cathode Materials for Advanced Zinc-Ion Aqueous Batteries.

Adv Sci (Weinh) 2020 Jan 19;8(1):2002722. Epub 2020 Nov 19.

Pillar of Engineering Product Development Singapore University of Technology and Design 8 Somapah Road Singapore 487372 Singapore.

Zinc-ion batteries (ZIBs) have attracted intensive attention due to the low cost, high safety, and abundant resources. However, up to date, challenges still exist in searching for cathode materials with high working potential, excellent electrochemical activity, and good structural stability. To address these challenges, microstructure engineering has been widely investigated to modulate the physical properties of cathode materials, and thus boosts the electrochemical performances of ZIBs. Here, the recent research efforts on the microstructural engineering of various ZIB cathode materials are mainly focused upon, including composition and crystal structure selection, crystal defect engineering, interlayer engineering, and morphology design. The dependency of cathode performance on aqueous electrolyte for ZIB is further discussed. Finally, future perspectives and challenges on microstructure engineering of cathode materials for ZIBs are provided. It is aimed to provide a deep understanding of the microstructure engineering effect on Zn storage performance.
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http://dx.doi.org/10.1002/advs.202002722DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7788579PMC
January 2020

Stormwater herbicides removal with a solar-driven advanced oxidation process: A feasibility investigation.

Water Res 2021 Feb 24;190:116783. Epub 2020 Dec 24.

School of Civil and Environmental Engineering, University of New South Wales, NSW 2052, Australia.

The solar driven advanced oxidation process (AOP) has the potential to be developed as a passive stormwater post-treatment method. Despite its widespread studies in wastewater treatment, the applicability of the process for micropollutant removal in stormwater (which has very different chemical properties from wastewater) is still unknown. This paper investigated the feasibility of three different AOP processes for the degradation of two herbicides (diuron and atrazine) in pre-treated stormwater: (i) photoelectrochemical oxidation (PECO), (ii) electrochemical oxidation (ECO), and (iii) photocatalytic oxidation (PCO). The durability of different anode materials, the effects of catalyst loading, and solar photo- and thermal impacts under different applied voltages were studied. Boron-doped diamond (BDD) was found to be the most durable anode material compared to carbon fiber and titanium foil for long-term operation. Due to the very low electroconductivity of stormwater, a high voltage was required, causing severe oxidation of the carbon fiber material. PECO achieved the best degradation results compared to ECO and PCO, with over 90% degradation of both herbicides in 2 h under 5 V, following a first-order decay process (with a half-life value of 0.40 h for diuron and 0.58 h for atrazine). The voltage increase had a positive impact on the oxidation processes, with 5 V found to be the optimal applied voltage, while catalyst loading had a negligible effect. Interestingly, the solar thermal effect plays a dominant role in enhancing the performance of the PECO process, which indicates the potential of integrating a photovoltaic chamber with a PECO system to harness both the light and heat of solar energy for stormwater treatment.
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http://dx.doi.org/10.1016/j.watres.2020.116783DOI Listing
February 2021

Industrial carbon dioxide capture and utilization: state of the art and future challenges.

Chem Soc Rev 2020 Dec 19;49(23):8584-8686. Epub 2020 Oct 19.

College of Environmental Science and Engineering, Beijing Forestry University, 35 Qinghua East Road, Haidian District, Beijing 100083, P. R. China.

Dramatically increased CO concentration from several point sources is perceived to cause severe greenhouse effect towards the serious ongoing global warming with associated climate destabilization, inducing undesirable natural calamities, melting of glaciers, and extreme weather patterns. CO capture and utilization (CCU) has received tremendous attention due to its significant role in intensifying global warming. Considering the lack of a timely review on the state-of-the-art progress of promising CCU techniques, developing an appropriate and prompt summary of such advanced techniques with a comprehensive understanding is necessary. Thus, it is imperative to provide a timely review, given the fast growth of sophisticated CO capture and utilization materials and their implementation. In this work, we critically summarized and comprehensively reviewed the characteristics and performance of both liquid and solid CO adsorbents with possible schemes for the improvement of their CO capture ability and advances in CO utilization. Their industrial applications in pre- and post-combustion CO capture as well as utilization were systematically discussed and compared. With our great effort, this review would be of significant importance for academic researchers for obtaining an overall understanding of the current developments and future trends of CCU. This work is bound to benefit researchers in fields relating to CCU and facilitate the progress of significant breakthroughs in both fundamental research and commercial applications to deliver perspective views for future scientific and industrial advances in CCU.
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http://dx.doi.org/10.1039/d0cs00025fDOI Listing
December 2020

Direct insights into the role of epoxy groups on cobalt sites for acidic HO production.

Nat Commun 2020 Aug 21;11(1):4181. Epub 2020 Aug 21.

Particles and Catalysis Research Group, School of Chemical Engineering, The University of New South Wales, Sydney, NSW, 2052, Australia.

Hydrogen peroxide produced by electrochemical oxygen reduction reaction provides a potentially cost effective and energy efficient alternative to the industrial anthraquinone process. In this study, we demonstrate that by modulating the oxygen functional groups near the atomically dispersed cobalt sites with proper electrochemical/chemical treatments, a highly active and selective oxygen reduction process for hydrogen peroxide production can be obtained in acidic electrolyte, showing a negligible amount of onset overpotential and nearly 100% selectivity within a wide range of applied potentials. Combined spectroscopic results reveal that the exceptionally enhanced performance of hydrogen peroxide generation originates from the presence of epoxy groups near the Co-N centers, which has resulted in the modification of the electronic structure of the cobalt atoms. Computational modeling demonstrates these electronically modified cobalt atoms will enhance the hydrogen peroxide productivity during oxygen reduction reaction in acid, providing insights into the design of electroactive materials for effective peroxide production.
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http://dx.doi.org/10.1038/s41467-020-17782-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7442824PMC
August 2020

Valence Alignment of Mixed Ni-Fe Hydroxide Electrocatalysts through Preferential Templating on Graphene Edges for Enhanced Oxygen Evolution.

ACS Nano 2020 Sep 18;14(9):11327-11340. Epub 2020 Aug 18.

School of Chemical Engineering, The University of New South Wales, Kensington, New South Wales 2052, Australia.

Engineering the metal-carbon heterointerface has become an increasingly important route toward achieving cost-effective and high-performing electrocatalysts. The specific properties of graphene edge sites, such as the high available density of states and extended unpaired π-bonding, make it a promising candidate to tune the electronic properties of metal catalysts. However, to date, understanding and leveraging graphene edge-metal catalysts for improved electrocatalytic performance remains largely elusive. Herein, edge-rich vertical graphene (er-VG) was synthesized and used as a catalyst support for Ni-Fe hydroxides for the oxygen evolution reaction (OER). The hybrid Ni-Fe/er-VG catalyst exhibits excellent OER performance with a mass current of 4051 A g (at overpotential η = 300 mV) and turnover frequency (TOF) of 4.8 s (η = 400 mV), outperforming Ni-Fe deposited on pristine VG and other metal foam supports. Angle-dependent X-ray absorption spectroscopy shows that the edge-rich VG support can preferentially template Fe-O units with a specific valence orbital alignment interacting with the unoccupied density of states on the graphene edges. This graphene edge-metal interaction was shown to facilitate the formation of undersaturated and strained Fe-sites with high valence states, while promoting the formation of redox-activated Ni species, thus improving OER performance. These findings demonstrate rational design of the graphene edge-metal interface in electrocatalysts which can be used for various energy conversion and chemical synthesis reactions.
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http://dx.doi.org/10.1021/acsnano.0c03380DOI Listing
September 2020

Dynamic single-site polysulfide immobilization in long-range disorder Cu-MOFs.

Chem Commun (Camb) 2020 Aug;56(69):10074-10077

Particles and Catalysis Research Laboratory, School of Chemical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. and UNSW Digital Grid Futures Institute, The University of New South Wales, Sydney, NSW 2052, Australia.

The structural transformation of MOFs in a polysulfide electrode process is poorly understood. We report the electrochemical amorphization of Cu3(BTC)2 MOFs in polysulfide electrolyte. We unveil the dynamic single-site polysulfide immobilization at the interconvertible Cu2+/Cu+ cation centres upon polysulfide adsorption and desorption, along with the reversible distortion of the Cu-O square planar unit.
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http://dx.doi.org/10.1039/d0cc04001kDOI Listing
August 2020

Bi-Sn Catalytic Foam Governed by Nanometallurgy of Liquid Metals.

Nano Lett 2020 Jun 7;20(6):4403-4409. Epub 2020 May 7.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney, New South Wales 2052, Australia.

Metallic foams, with intrinsic catalytic properties, are critical for heterogeneous catalysis reactions and reactor designs. Market ready catalytic foams are costly and made of multimaterial coatings with large sub-millimeter open cells providing insufficient active surface area. Here we use the principle of nanometallurgy within liquid metals to prepare nanostructured catalytic metal foams using a low-cost alloy of bismuth and tin with sub-micrometer open cells. The eutectic bismuth and tin liquid metal alloy was processed into nanoparticles and blown into a tin and bismuth nanophase separated heterostructure in aqueous media at room temperature and using an indium brazing agent. The CO electroconversion efficiency of the catalytic foam is presented with an impressive 82% conversion efficiency toward formates at high current density of -25 mA cm (-1.2 V vs RHE). Nanometallurgical process applied to liquid metals will lead to exciting possibilities for expanding industrial and research accessibility of catalytic foams.
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http://dx.doi.org/10.1021/acs.nanolett.0c01170DOI Listing
June 2020

Synergistic ultraviolet and visible light photo-activation enables intensified low-temperature methanol synthesis over copper/zinc oxide/alumina.

Nat Commun 2020 Mar 31;11(1):1615. Epub 2020 Mar 31.

School of Chemical Engineering, UNSW Australia, Sydney, NSW, 2052, Australia.

Although photoexcitation has been employed to unlock the low-temperature equilibrium regimes of thermal catalysis, mechanism underlining potential interplay between electron excitations and surface chemical processes remains elusive. Here, we report an associative zinc oxide band-gap excitation and copper plasmonic excitation that can cooperatively promote methanol-production at the copper-zinc oxide interfacial perimeter of copper/zinc oxide/alumina (CZA) catalyst. Conversely, selective excitation of individual components only leads to the promotion of carbon monoxide production. Accompanied by the variation in surface copper oxidation state and local electronic structure of zinc, electrons originating from the zinc oxide excitation and copper plasmonic excitation serve to activate surface adsorbates, catalysing key elementary processes (namely formate conversion and hydrogen molecule activation), thus providing one explanation for the observed photothermal activity. These observations give valuable insights into the key elementary processes occurring on the surface of the CZA catalyst under light-heat dual activation.
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http://dx.doi.org/10.1038/s41467-020-15445-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7109065PMC
March 2020

Tunable Syngas Production through CO Electroreduction on Cobalt-Carbon Composite Electrocatalyst.

ACS Appl Mater Interfaces 2020 Feb 14;12(8):9307-9315. Epub 2020 Feb 14.

Particles and Catalysis Research Laboratory, School of Chemical Engineering , The University of New South Wales , Sydney , New South Wales 2052 , Australia.

Controllable concomitant production of CO and H (syngas) during electrochemical CO reduction reactions (CORR) is expected to improve the commercial feasibility of the technology to mitigate CO emissions as the generated syngas can be converted into useful chemicals using the commercial Fischer-Tropsch (FT) process. Herein, we demonstrate the ability of a Co single-atom-decorated N-doped graphitic carbon shell-encapsulated cobalt nanoparticle electrocatalyst (referred as [email protected]) to controllably produce syngas at low overpotentials during CORR. Through the engineering and modulation of dual active sites for CORR (modified carbon shell with encapsulated Co) and hydrogen evolution reaction (Co-N moieties) within [email protected] by varying the annealing temperature, we are able to tune the H: CO ratio from 1: 2 to 1: 1 to 3: 2 over a wide range of applied potentials (-0.5 V to -0.8 V versus reversible hydrogen electrode, RHE). This versatile control of H: CO ratio in CORR reaction brings up significant opportunity of using CO and HO and renewable energy for producing a range of chemicals.
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http://dx.doi.org/10.1021/acsami.9b21216DOI Listing
February 2020

From passivation to activation - tunable nickel/nickel oxide for hydrogen evolution electrocatalysis.

Chem Commun (Camb) 2020 Feb;56(11):1709-1712

Particle and Catalysis Research Group, School of Chemical Engineering, University of New South Wales, 2052, NSW, Australia.

A novel, simple and controllable approach to designing NiO/Ni heterostructures supported on carbon for the hydrogen evolution reaction (HER) was utilized. By selectively oxidizing the Ni deposits, to differing degrees, the benefits of the NiO/Ni heterostructures were elucidated with the extent of Ni oxidation being a key factor in dictating performance.
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http://dx.doi.org/10.1039/c9cc07486dDOI Listing
February 2020

Heritable nanosilver resistance in priority pathogen: a unique genetic adaptation and comparison with ionic silver and antibiotics.

Nanoscale 2020 Jan 13;12(4):2384-2392. Epub 2020 Jan 13.

Ithree institute, University of Technology Sydney, NSW 2007, Australia. and School of Chemical Engineering, University of New South Wales, Sydney, NSW 2052, Australia.

The past decade has seen the incorporation of antimicrobial nanosilver (NAg) into medical devices, and, increasingly, in everyday 'antibacterial' products. With the continued rise of antibiotic resistant bacteria, there are concerns that these priority pathogens will also develop resistance to the extensively commercialized nanoparticle antimicrobials. Herein, this work reports the emergence of stable resistance traits to NAg in the WHO-listed priority pathogen Staphylococcus aureus, which has previously been suggested to have no, or very low, capacity for silver resistance. With no native presence of genetically encoded silver defence mechanisms, the work showed that the bacterium is dependent on mutation of physiologically essential genes, including those involved in nucleotide synthesis and oxidative stress defence. While some mutations were uniquely associated with resistance to NAg, the study also found common mutations that could be protective against both NAg and ionic silver. This is consistent with the observation of NAg/ionic silver cross-resistance. These mutations were detected following withdrawal of the silver exposure, denoting heritable characteristics that allow for spread of the resistance traits even with discontinued silver use. Heritable silver resistance in priority pathogen cautions that these nanoparticle antimicrobials should only be used as needed, to preserve their efficacy for treating infections.
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http://dx.doi.org/10.1039/c9nr08424jDOI Listing
January 2020

Nanosilver Targets the Bacterial Cell Envelope: The Link with Generation of Reactive Oxygen Radicals.

ACS Appl Mater Interfaces 2020 Feb 23;12(5):5557-5568. Epub 2020 Jan 23.

School of Chemical Engineering , University of New South Wales , Sydney , NSW 2052 , Australia.

The work describes the interactions of nanosilver (NAg) with bacterial cell envelope components at a molecular level and how this associates with the reactive oxygen species (ROS)-mediated toxicity of the nanoparticle. Major structural changes were detected in cell envelope biomolecules as a result of damages in functional moieties, such as the saccharides, amides, and phosphodiesters. NAg exposure disintegrates the glycan backbone in the major cell wall component peptidoglycan, causes complete breakdown of lipoteichoic acid, and disrupts the phosphate-amine and fatty acid groups in phosphatidylethanolamine, a membrane phospholipid. Consistent with the oxidative attacks, we propose that the observed cell envelope damages are inflicted, at least in part, by the reactive oxygen radicals being generated by the nanoparticle during its leaching process, abiotically, without cells. The cell envelope targeting, especially those on the inner membrane phospholipid, is likely to then trigger the rapid generation of lethal levels of cellular superoxide (O) and hydroxyl (OH) radicals herein seen with a model bacterium. The present study provides a better understanding of the antibacterial mechanisms of NAg, whereby ROS generation could be both the cause and consequence of the toxicity, associated with the initial cell envelope targeting by the nanoparticle.
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http://dx.doi.org/10.1021/acsami.9b20193DOI Listing
February 2020

Photocatalytic and Photoelectrochemical Systems: Similarities and Differences.

Adv Mater 2020 May 9;32(18):e1904717. Epub 2019 Dec 9.

Particles and Catalysis Research Group, School of Chemical Engineering, The University of New South Wales, Sydney, NSW, 2052, Australia.

Photocatalytic and photoelectrochemical processes are two key systems in harvesting sunlight for energy and environmental applications. As both systems are employing photoactive semiconductors as the major active component, strategies have been formulated to improve the properties of the semiconductors for better performances. However, requirements to yield excellent performances are different in these two distinctive systems. Although there are universal strategies applicable to improve the performance of photoactive semiconductors, similarities and differences exist when the semiconductors are to be used differently. Here, considerations on selected typical factors governing the performances in photocatalytic and photoelectrochemical systems, even though the same type of semiconductor is used, are provided. Understanding of the underlying mechanisms in relation to their photoactivities is of fundamental importance for rational design of high-performing photoactive materials, which may serve as a general guideline for the fabrication of good photocatalysts or photoelectrodes toward sustainable solar fuel generation.
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http://dx.doi.org/10.1002/adma.201904717DOI Listing
May 2020

Advantages of eutectic alloys for creating catalysts in the realm of nanotechnology-enabled metallurgy.

Nat Commun 2019 10 11;10(1):4645. Epub 2019 Oct 11.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney, NSW, 2052, Australia.

The nascent field of nanotechnology-enabled metallurgy has great potential. However, the role of eutectic alloys and the nature of alloy solidification in this field are still largely unknown. To demonstrate one of the promises of liquid metals in the field, we explore a model system of catalytically active Bi-Sn nano-alloys produced using a liquid-phase ultrasonication technique and investigate their phase separation, surface oxidation, and nucleation. The Bi-Sn ratio determines the grain boundary properties and the emergence of dislocations within the nano-alloys. The eutectic system gives rise to the smallest grain dimensions among all Bi-Sn ratios along with more pronounced dislocation formation within the nano-alloys. Using electrochemical CO reduction and photocatalysis, we demonstrate that the structural peculiarity of the eutectic nano-alloys offers the highest catalytic activity in comparison with their non-eutectic counterparts. The fundamentals of nano-alloy formation revealed here may establish the groundwork for creating bimetallic and multimetallic nano-alloys.
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http://dx.doi.org/10.1038/s41467-019-12615-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6789138PMC
October 2019

Surface strategies for catalytic CO reduction: from two-dimensional materials to nanoclusters to single atoms.

Chem Soc Rev 2019 Oct;48(21):5310-5349

Research School of Chemistry, Australian National University, ACT 2601, Australia.

Redox catalysis, including photocatalysis and (photo)electrocatalysis, may alleviate global warming and energy crises by removing excess CO2 from the atmosphere and converting it to value-added resources. Nano-to-atomic two-dimensional (2D) materials, clusters and single atoms are superior catalysts because of their engineerable ultrathin/small dimensions and large surface areas and have attracted worldwide research interest. Given the current gap between research and applications in CO2 reduction, our review systematically and constructively discusses nano-to-atomic surface strategies for catalysts reported to date. This work is expected to drive and benefit future research to rationally design surface strategies with multi-parameter synergistic impacts on the selectivity, activity and stability of next-generation CO2 reduction catalysts, thus opening new avenues for sustainable solutions to climate change, energy and environmental issues, and the potential industrial economy.
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http://dx.doi.org/10.1039/c9cs00163hDOI Listing
October 2019

Modulating Activity through Defect Engineering of Tin Oxides for Electrochemical CO Reduction.

Adv Sci (Weinh) 2019 Sep 4;6(18):1900678. Epub 2019 Jul 4.

Particles and Catalysis Research Laboratory School of Chemical Engineering The University of New South Wales Sydney NSW 2052 Australia.

The large-scale application of electrochemical reduction of CO, as a viable strategy to mitigate the effects of anthropogenic climate change, is hindered by the lack of active and cost-effective electrocatalysts that can be generated in bulk. To this end, SnO nanoparticles that are prepared using the industrially adopted flame spray pyrolysis (FSP) technique as active catalysts are reported for the conversion of CO to formate (HCOO), exhibiting a FE of 85% with a current density of -23.7 mA cm at an applied potential of -1.1 V versus reversible hydrogen electrode. Through tuning of the flame synthesis conditions, the amount of oxygen hole center (OHC; Sn≡O●) is synthetically manipulated, which plays a vital role in CO activation and thereby governing the high activity displayed by the FSP-SnO catalysts for formate production. The controlled generation of defects through a simple, scalable fabrication technique presents an ideal approach for rationally designing active CO reduction reactions catalysts.
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http://dx.doi.org/10.1002/advs.201900678DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6755522PMC
September 2019

Plasma Treating Mixed Metal Oxides to Improve Oxidative Performance via Defect Generation.

Materials (Basel) 2019 Aug 27;12(17). Epub 2019 Aug 27.

School of Chemical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia.

The generation of structural defects in metal oxide catalysts offers a potential pathway to improve performance. Herein, we investigated the effect of thermal hydrogenation and low-temperature plasma treatments on mixed SiO/TiO materials. Hydrogenation at 500 °C resulted in the reduction of the material to produce Ti in the bulk TiO. In contrast, low temperature plasma treatment for 10 or 20 min generated surface Ti species via the removal of oxygen on both the neat and hydrogenated material. Assessing the photocatalytic activity of the materials demonstrated a 40-130% increase in the rate of formic acid oxidation after plasma treatment. A strong relationship between the Ti content and catalyst activity was established, although a change in the Si-Ti interaction after plasma treating of the neat SiO/TiO material was found to limit performance, and suggests that performance is not determined solely by the presence of Ti.
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http://dx.doi.org/10.3390/ma12172756DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6747793PMC
August 2019

Oxygen-Vacancy Engineering of Cerium-Oxide Nanoparticles for Antioxidant Activity.

ACS Omega 2019 May 30;4(5):9473-9479. Epub 2019 May 30.

Particles and Catalysis Research Group, School of Chemical Engineering, and Graduate School of Biomedical Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia.

To address an important challenge in the engineering of antioxidant nanoparticles, the present work devised a surface-to-bulk migration of oxygen vacancies in the oxygen radical-scavenging cerium-oxide nanoparticles. The study highlights the significance of surface oxygen vacancies in the intended cellular internalization and, subsequently, the radical scavenging activity of the nanoparticles inside the cells. The findings advise future development of therapeutic antioxidant nanomaterials to also include engineering of the particles for enhanced surface defects not only for the accessibility of their oxygen vacancies but also, equally important, rendering them bioavailable for cellular uptake.
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http://dx.doi.org/10.1021/acsomega.9b00521DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6648134PMC
May 2019

Asymmetrical Double Flame Spray Pyrolysis-Designed SiO/CeZrO for the Dry Reforming of Methane.

ACS Appl Mater Interfaces 2019 Jul 12;11(29):25766-25777. Epub 2019 Jul 12.

Particles and Catalysis Group, School of Chemical Engineering , The University of New South Wales , Sydney , NSW 2052 , Australia.

Silica has the potential to enhance the performance of ceria-zirconia as a support for the dry reforming of methane; however, controlling the integration of silica with the ceria-zirconia using flame spray pyrolysis (FSP) is a significant challenge. To address this challenge, an asymmetrically variable double-FSP (DFSP) system was established to control the SiO interaction with CeZrO. The engineered materials were then utilized as supports for Ni for the dry reforming of methane. Initially, silica formation during FSP synthesis was examined where it was revealed that, at a low precursor concentration (<1.5 M tetraethyl orthosilicate in xylenes), the physical characteristics of the silica varied differently in relation to what is typically encountered during FSP synthesis. Explicitly, on using a 0.5 M tetraethyl orthosilicate precursor, increasing the FSP feed rate provided an increase in the specific surface area from 217 m/g at 3 mL/min to 363 m/g at 7 mL/min. Adopting this knowledge on silica formation under these conditions, the asymmetrical DFSP system was then exploited to regulate the integration of ceria-zirconia with the silica. To restrict the silica from coating the particles during DFSP, the intersection distance along the silica flame was tuned from 18.5 to 28.5 cm, whereas the distance along the ceria-zirconia flame was fixed at 5 cm. It was found that at short intersection distances the ceria-zirconia provided sites for silica nucleation and growth, resulting in high surface-area silica encapsulating the ceria-zirconia. At large intersection distances, encapsulation of the ceria-zirconia by silica was suppressed. An enhanced oxygen storage capacity and basicity along with the small Ni sizes facilitated by the longer intersection distances produced the most selective catalyst for the dry reforming of methane.
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http://dx.doi.org/10.1021/acsami.9b02572DOI Listing
July 2019

The Importance of the Interfacial Contact: Is Reduced Graphene Oxide Always an Enhancer in Photo(Electro)Catalytic Water Oxidation?

ACS Appl Mater Interfaces 2019 Jul 18;11(26):23125-23134. Epub 2019 Jun 18.

School of Energy and Environment , City University of Hong Kong , Kowloon , Hong Kong SAR.

Optimizing interfacial contact between graphene and a semiconductor has often been proposed as essential for improving their charge interactions. Herein, we fabricated bismuth vanadate-reduced graphene oxide (BiVO/rGO) composites with tailored interfacial contact extents and revealed their disparate behavior in photoelectrochemical (PEC) and powder suspension (PS) water oxidation systems. BiVO/rGO with a high rGO coverage on the BiVO surface (BiVO/rGO HC) exhibited an 8-fold enhancement in the PEC photocurrent density with respect to neat BiVO at 0 V versus Ag/AgCl, while BiVO/rGO with a low rGO coverage (BiVO/rGO LC) gave a lesser 3-fold enhancement. In contrast, BiVO/rGO HC delivered a detrimental effect, while BiVO/rGO LC exhibited an enhanced performance for oxygen evolution in the PS system. The phenomenon is attributed to changes in the hydrophobicity of the BiVO/rGO composite in conjunction with the interfacial contact configuration. A better BiVO/rGO interfacial contact was found to improve the charge separation efficiency and charge transfer ability of the composite material, explaining the superior PEC performance of BiVO/rGO HC. Additionally, optimization of the interfacial contact extent was revealed to further improve the energetics of the composite material, as evidenced by a Fermi level shift to a more negative potential. However, the high hydrophobicity of BiVO/rGO HC arising from the higher rGO reduction extent triggered poor water miscibility, reducing the surface wettability and therefore hampering the photocatalytic O evolution activity of the sample. The study underlines water miscibility as a governing issue in the PS system.
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http://dx.doi.org/10.1021/acsami.9b03624DOI Listing
July 2019

Spherical Murray-Type Assembly of Co-N-C Nanoparticles as a High-Performance Trifunctional Electrocatalyst.

ACS Appl Mater Interfaces 2019 Mar 1;11(10):9925-9933. Epub 2019 Mar 1.

Particles and Catalysis Research Group, School of Chemical Engineering , The University of New South Wales , Sydney , New South Wales 2052 , Australia.

Future renewable energy conversion requires advanced electrocatalysis technologies for hydrogen production, fuel cells, and metal-air batteries. Highly efficient trifunctional nonprecious electrocatalysts are a critical precious metal replacement for the economically viable electrocatalysis of oxygen reduction and water splitting, both of which are a triphase electrode process. Electrocatalysts with a refined porous structure and active composition beneficial for three-phase reactions are broadly pursued. Herein, a highly promising trifunctional spherical Murray assembly of Co-N-C nanoparticles was derived from low-cost Prussian blue analogues for the oxygen reduction reaction and water splitting. The Murray-type architecture with a tunable porous hierarchy for efficient mass transfer and the combination of a Co-N-C active composition are key for the improved electrocatalytic performance. Acid-leaching produced an optimized Murray-type durable and methanol-tolerant Co-N-C electrocatalyst that achieved an onset potential of 0.94 V [vs reversible hydrogen electrode (RHE)] and a half wave potential of 0.84 V (vs RHE) as well as a large diffusion-limited current density of 5.7 mA cm for the oxygen reduction reaction, which is comparable to Pt/C. In addition, it displayed low onset overpotentials of ∼150 and ∼350 mV corresponding to the hydrogen evolution reaction and oxygen evolution reaction, respectively, highlighting its great potential to be used in overall water splitting with a total splitting voltage of 1.73 V. This work highlights the importance of Murray-type electrocatalysts for multiphase energy-related reactions.
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http://dx.doi.org/10.1021/acsami.8b20565DOI Listing
March 2019

Unlocking high-potential non-persistent radical chemistry for semi-aqueous redox batteries.

Chem Commun (Camb) 2019 Feb;55(15):2154-2157

School of Chemical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia.

A non-persistent radical precursor, N-hydroxyphthalimide (NHPI), is reported as a low-cost, high-potential organic cathode in a binary electrolyte for a semi-aqueous redox battery. A highly reversible NHPI-phthalimide N-oxyl (PINO) radical redox couple at +1.30 VNHE is demonstrated, providing a 1.15 V rechargeable battery with an attractive >85% voltage efficiency when coupled with anthraquinone-2-sulfonic acid (AQS).
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http://dx.doi.org/10.1039/c8cc09304kDOI Listing
February 2019
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