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Phase shuttling of Pb3O4 leads to the reconstructed β-PbO2 phase and significantly enhances the electrochemical ozone production (EOP) through water oxidation.

The reaction kinetics of spin-polarized oxygen evolution reaction (OER) can be enhanced by ferromagnetic (FM) catalysts under an external magnetic field. However, applying a magnetic field necessitates additional energy consumption and creates design difficulties for OER. Herein, we demonstrate that a single-domain FM catalyst without external magnetic fields exhibits a similar OER increment to its magnetized multi-domain one. The evidence is given by comparing the pH-dependent increment of OER on multi- and single-domain FM catalysts with or without a magnetic field. The intrinsic activity of a single-domain catalyst is higher than that of a multi-domain counterpart. The latter can be promoted to approach the former by the magnetization effect. Reducing the FM catalyst size into the single-domain region, the spin-polarized OER performance can be achieved without a magnetic field, illustrating an external magnetic field is not a requirement to reap the benefits of magnetic catalysts. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version This work is supported by the Singapore MOE Tier 2 grant (MOE-T2EP10220-0001) and the Singapore National Research Foundation under its Campus for Research Excellence and Technological Enterprise (CREATE) programme.

Electrochemical water splitting consists of two elementary reactions i.e., hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Developing robust HER and OER technologies necessitates a molecular picture of reaction mechanism, yet the reactants for water splitting reactions are unfortunately not fully understood. Here we utilize magnetic field to understand proton transport in HER, and hydroxide ion transport in OER, to discuss the possible implications on understanding the reactants for HER and OER. Magnetic field is a known tool for changing the movement of charged species like ions, e.g. the magnetic-field-improved Cu2+ transportation near the electrode in Cu electrodeposition. However, applying a magnetic field does not affect the HER or OER rate across various pH, which challenges the traditional opinion that charged species (i.e. proton and hydroxide ion) act as the reactant. This anomalous response of HER and OER to magnetic field, and the fact that the transport of proton and hydroxide ion follow Grotthuss mechanism, collectively indicate water may act as the universal reactant for HER and OER across various pH. With the aid of magnetic field, this work serves as an understanding of water might be the reactant in HER and OER, and possibly in other electrocatalysis reactions involving protonation and deprotonation step. A model that simply focuses on the charged species but overlooking the complexity of the whole electrolyte phase where water is the dominant species, may not reasonably reflect the electrochemistry of HER and OER in aqueous electrolyte.

While palladium-based catalysts are effective in low-temperature methane combustion, their high cost and scarcity render them unsuitable to fulfil the growing demand. The design of improved catalysts which can more efficiently utilize this precious metal is required. Here, by using a facile one-pot thermal decomposition method Pd-NiCo2O4 spinel catalysts with a unique structure are obtained, in which the majority of Pd incorporated into the bulk spinel structure of NiCo2O4 with limited highly dispersed PdOx species on the surface at an atomic scale. The robust 1 %Pd-NiCo2O4 spinel catalyst exhibits comparable activity in methane oxidation to that of the conventional incipient wetness impregnation 2 %Pd/NiCo2O4. Theoretical calculations and catalyst characterizations (SEM, HRTEM, XRD, XPS, XAS, ICP-OES, etc.) revealed that the enhanced activity is mainly originated from having the O p-band center closer to the Fermi level, with Pd ions incorporated into the bulk NiCo2O4 via substituting for the octahedral coordinated Ni3+/Co3+.

The efficiency of electrolytic hydrogen production is limited by the slow reaction kinetics of oxygen evolution reaction (OER). Surface-reconstructed ferromagnetic (FM) catalysts with a spin-pinning effect at the FM/oxyhydroxide interface could enhance the spin-dependent OER kinetics. However, in real-life applications, electrolyzers are operated at elevated temperature, which may disrupt the spin orientations of FM catalysts and limit their performance. In this study, we prepared surface-reconstructed SmCo5 /CoOx Hy , which possesses polarized spins at the FM/oxyhydroxide interface that lead to excellent OER activity. These interfacial polarized spins could be further aligned through a magnetization process, which further enhanced the OER performance. Moreover, the operation temperature was elevated to mimic the practical operation conditions of water electrolyzers. It was found that the OER activity enhancement of the magnetized SmCo5 /CoOx Hy catalyst could be preserved up to 60 °C.

The evaluation of the intrinsic activity of catalysts is the most basic in searching energy- and cost-efficient catalyst materials for various applications. The accurate determination of the intrinsic activity is essential for identifying efficient catalysts. While a huge number of studies of electrocatalysis for various applications have been reported, the effects of electrode loading on the apparent intrinsic activity obtained experimentally have been rarely discussed. With a high mass loading on the electrode, not all the catalyst surfaces can be electrochemically active because not all the surfaces can be wetted by the electrolyte. The loading also affects the transport of electrons over the electrode as well as the transport of ions in the electrolyte, and thus affects the kinetics. These lead to the derivations of the apparent intrinsic activity from the real intrinsic activity. Herein, for better understanding the derivations, we evaluate and discuss the effects of electrode mass loading using oxygen evolution reaction as an example.

Water electrolysis is a promising technique for carbon neutral hydrogen production. A great challenge remains at developing robust and low-cost anode catalysts. Many pre-catalysts are found to undergo surface reconstruction to give high intrinsic activity in the oxygen evolution reaction (OER). The reconstructed oxyhydroxides on the surface are active species and most of them outperform directly synthesized oxyhydroxides. The reason for the high intrinsic activity remains to be explored. Here, a study is reported to showcase the unique reconstruction behaviors of a pre-catalyst, thiospinel CoFe2 S4 , and its reconstruction chemistry for a high OER activity. The reconstruction of CoFe2 S4 gives a mixture with both Fe-S component and active oxyhydroxide (Co(Fe)Ox Hy ) because Co is more inclined to reconstruct as oxyhydroxide, while the Fe is more stable in Fe-S component in a major form of Fe3 S4 . The interface spin channel is demonstrated in the reconstructed CoFe2 S4 , which optimizes the energetics of OER steps on Co(Fe)Ox Hy species and facilitates the spin sensitive electron transfer to reduce the kinetic barrier of O-O coupling. The advantage is also demonstrated in a membrane electrode assembly (MEA) electrolyzer. This work introduces the feasibility of engineering the reconstruction chemistry of the precatalyst for high performance and durable MEA electrolyzers. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version The authors thank the support from the Singapore Ministry of Education Tier 2 Grant (MOE-T2EP10220-0001) and the Singapore National Research Foundation under its Campus for Research Excellence and Technological Enterprise (CREATE) programme, through the Cambridge Center for Carbon Reduction in Chemical Technology (C4T) and eCO2EP programmes.

This article presents a study on the effect of the hydroxyl group position on the electro-oxidation of butanediols, including 1,2-butanediol, 2,3-butanediol, 1,3-butanediol, and 1,4-butanediol. The effect of the hydroxyl group position in butanediols on their electro-oxidation reactivities is investigated by cyclic voltammetry, linear sweep voltammetry, chronopotentiometry and chronoamperometry in 1.0 M KOH. The results show that the closer the two hydroxyl groups are, the higher the reactivity, and the lower the anodic potential butanediol has. Moreover, the oxidation products from chronoamperometry are analyzed by means of HPLC and NMR. Some value-added products, such as 3-hydroxypropionic acid/3-hydroxypropionate, are produced. The DFT calculation indicates that the oxidation of vicinal diols responds to the conversion from a hydroxyl group to a carboxylate group, followed by C-C bond cleavage, where the carbon charge decreases. These results provide an insight into reactant selection for the electrochemical synthesis of value-added chemicals. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Published version This work was supported by the Singapore Ministry of Education Tier 2 Grants (MOE-T2EP10220-0001), the Singapore National Research Foundation under its Campus for Research Excellence and Technological Enterprise (CREATE) programme and NRF Fellowship (NRF-NRFF2017-04), the Centre of Advanced Catalysis Science and Technology, Nanyang Technological University, and the Agency for Science, Technology and Research (Central Research Fund Award).

Spinel zinc cobalt oxide (ZnCo2 O4 ) is not considered as a superior catalyst for the electrochemical oxygen evolution reaction (OER), which is the bottleneck reaction in water-electrolysis. Herein, taking advantage of density functional theory (DFT) calculations, we find that the existence of low-spin (LS) state cobalt cations hinders the OER activity of spinel zinc cobalt oxide, as the t2g 6 eg 0 configuration gives rise to purely localized electronic structure and exhibits poor binding affinity to the key reaction intermediate. Increasing the spin state of cobalt cations in spinel ZnCo2 O4 is found to propagate a spin channel to promote spin-selected charge transport during OER and generate better active sites for intermediates adsorption. The experiments find increasing the calcination temperature a facile approach to engineer high-spin (HS) state cobalt cations in ZnCo2 O4 , while not working for Co3 O4 . The activity of the best spin-state-engineered ZnCo2 O4 outperforms other typical Co-based oxides. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version Dr. S. Sun thanks the funding support from Beijing Natural Science Foundation Program 2212029 and National Natural Science Foundation of China-Youth Science Fund (Grant No. 52001009). All authors thank the Facility for Analysis, Characterisation, Testing and Simulation (FACTS) at the Nanyang Technological University for materials characterizations. This work was supported by Singapore Ministry of Education Tier 2 Grant (MOE2018-T2-2-027), the National Research Foundation, Prime Minister's Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme.

Proton exchange membrane water electrolyzer (PEMWE) is a major enabler of green hydrogen production. The development of water electrolyzers is a vital step in driving the progress of a hydrogen-based economy. The system inside the electrolyzer is a zero-gap cell featuring low ohmic resistance and boosted mass transport, leading to higher energy efficiency and minimized capital cost. Besides, utilizing PEM in the electrolyzer for sustainable hydrogen production enables the system to perform with many advantages, including superior energy efficiency, higher hydrogen purity, and high flexibility. Therefore, as PEM electrolyzers continue to evolve, sustainable hydrogen production on a larger scale will be realized in the near future. This review summarizes the status quo of PEM water electrolyzers in the past four years. We will start with a brief introduction of the core of a water electrolyzer, namely the membrane electrode assembly (MEA), which will be followed by an introduction of fabrication methods of MEA, including CCM methods, catalyst-coated electrode methods, and other innovative fabrication methods. Next, we will summarize recent attempts to modify electrodes and membranes in MEAs to promote the performance of PEMWE. Subsequently, catalyst development for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in MEA is discussed, highlighting novel HER/OER catalysts and strategies to reduce the content of noble metals. Lastly, conclusion and perspectives are provided to present a blueprint to inspire the future development of PEMWE.

A highly efficient and stable oxygen evolution reaction (OER) plays a key role in the commercialization of proton exchange membrane (PEM) water electrolyzers. Perovskite-derived IrO x H y catalysts have been demonstrated to be highly catalytically active in a harsh acidic environment. On the other hand, the inevitable degradation of the PEM can induce the release of sulfate ions, which could poison electrocatalysts. Herein, the poisoning effects of sulfate ions on a representative SrCo0.9Ir0.1O3-δ -derived IrO x H y catalyst and a standard IrO2 are studied. It is found that, besides sulfate ion adsorption on Ir active sites impacting both Ir-based catalysts, SrSO4 precipitation is the most prominent cause of activity degradation of IrO x H y . This phenomenon is unique to a reconstructed surface undergoing continuous cation leaching from the perovskite-oxyhydroxide interface, in which SrSO4 precipitate blocks electrolyte-accessible IrO x H y -walled channels, preventing further Sr and Co ion leaching from the interface and dehydrating the isolated portion of the blocked channels, resulting in a reduction in the number of Ir active sites and causing the catalyst to have an OER performance stability inferior to commercial IrO2.

A rational design on oxygen evolution reaction (OER) catalysts is pivotal to the overall efficiency of water electrolysis. Numerous works have been devoted to understanding the cation leaching and surface reconstruction of some very active electrocatalysts, while few have been on intentionally promoting the surface in a controlled fashion. In this work, we report controllable anodic leaching of Cr in CoCr2O4 by activating the pristine material at high potential, which enables the transformation of inactive spinel CoCr2O4 into a highly active catalyst. The depletion of Cr and consumption of lattice oxygen facilitate surface defects and oxygen vacancies, exposing Co species to reconstruct into active Co oxyhydroxides differ from CoOOH. A novel mechanism with the evolution of tetrahedrally coordinated surface cation into octahedral configuration via non-concerted proton-electron transfer is proposed. This work shows the importance of controlled anodic potential in modifying the surface chemistry of electrocatalysts. Ministry of Education (MOE) Accepted version The authors thank the Facility for Analysis,Characterization, Testingand Simulation (FACTS) in Nanyang Technological Univer-sity for materials characterization.

Perovskite oxides based on earth-abundant transition metals have been extensively explored as promising oxygen evolution reaction (OER) catalysts in alkaline media. The (electro)chemically induced transformation of their initially crystalline surface into an amorphous state has been reported for a few highly active perovskite catalysts. However, little knowledge is available to distinguish the contribution of the amorphized surface from that of the remaining bulk toward the OER. In this work, we utilize the promoting effects of two types of Fe modification, i.e., bulk Fe dopant and Fe ions absorbed from the electrolyte, on the OER activity of SrCoO3-δ model perovskite to identify the active phase. Transmission electron microscopy and X-ray photoelectron spectroscopy confirmed the surface amorphization of SrCoO3-δ as well as SrCo0.8Fe0.2O3-δ after potential cycling in Fe-free KOH solution. By further cycling in Fe-spiked electrolyte, Fe was incorporated into the amorphized surface of SrCoO3-δ (SrCoO3-δ + Fe3+), yielding approximately sixfold increase in activity. Despite the difference in remaining perovskites, SrCoO3-δ + Fe3+ and SrCo0.8Fe0.2O3-δ exhibited remarkably similar activity. These results reflect that the in situ developed surface species are directly responsible for the measured OER activity, whereas the remaining bulk phases have little impact.

The efficiency of electrocatalytic reactions has been continuously improved in recent years due to the great effort in the development of electrocatalysts. A popular strategy is engineering the size of electrocatalysts for better electrochemical performance and lower cost. Nanosized electrocatalysts with high specific surface area have been widely used in state-of-the-art electrochemical devices such as fuel cells. From an engineering aspect, nanosizing electrocatalysts increases the surface area of the electrode and improves the electrode/device performance. Beyond an engineering scope, this perspective highlights the size effects of certain scientific fundamentals in electrocatalytic reactions. The paper summarizes the representative examples in studying the size effects of electrocatalysts and sheds light on the change of intrinsic properties of electrocatalysts caused by the size variation. The size effects of electrocatalysts should be investigated in terms of both engineering and fundamental aspects; that is, the observed activity change is more than a result of surface area variation, and it is interesting to investigate the link between the intrinsic activity and the properties of the catalysts.

Developing new strategies to advance the fundamental understanding of electrochemistry is crucial to mitigating multiple contemporary technological challenges. In this regard, magnetoelectrochemistry offers many strategic advantages in controlling and understanding electrochemical reactions that might be tricky to regulate in conventional electrochemical fields. However, the topic is highly interdisciplinary, combining concepts from electrochemistry, hydrodynamics, and magnetism with experimental outcomes that are sometimes unexpected. In this Review, we survey recent advances in using a magnetic field in different electrochemical applications organized by the effect of the generated forces on fundamental electrochemical principles and focus on how the magnetic field leads to the observed results. Finally, we discuss the challenges that remain to be addressed to establish robust applications capable of meeting present needs. Ministry of Education (MOE) National Research Foundation (NRF) Published version The authors thank and acknowledge support from the Singapore Ministry of Education Tier 2 Grant (MOE-T2EP10220-0001), Tier 1 Grant (RG62/21). This research was also supported by the National Research Foundation, Prime Minister’s Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) program.

Porous boron nitride (BN) nanorods, which were synthesized via a one-stage pyrolysis, exhibited excellent catalytic performance for organics' degradation via peroxymonosulfate (PMS) activation. The origin of the unexpected catalytic function of porous BN nanorods was proposed, in which non-radical oxidation driven by the defects on porous BN dominated the sulfamethoxazole degradation via the generation of singlet oxygen (1O2). The adsorption energy between PMS and BN was calculated via density functional theory (DFT), and the PMS activation kinetics were further investigated using an electrochemical methodology. The evolution of 1O2 was verified by electron spin resonance (ESR) and chemical scavenging experiments. The observed non-radical oxidation presented a high robustness in different water matrices, combined with a series of much less toxic intermediates. The used BN was easily regenerated by heating in air, in which the B-O bond was fully recovered. These findings provide new insights for BN as a non-metal catalyst for organics' degradation via PMS activation, in both theoretical and practical prospects.

The rational design of efficient catalysts can be guided by identifying proper descriptors that can rationalize and predict the catalytic behaviors. This study presents the feasibility of using the relative position between O p-band center and B-site metal cation d-band center as an activity descriptor for methane oxidation over LaCoO3 perovskite oxides. Experiments on B-site substituted LaFexCo1-xO3 perovskite oxides revealed that the relative positions between the two band centers governed the catalytic comportment. The suprafacial model-driven catalysts with negative relative position values exhibited exceeding activity at low temperatures; Inversely, the intrafacial model-driven catalysts with positive relative position values, showed superior activity at high temperatures. These findings were found to be effective on the A-site substituted La1-xSrxCoO3 perovskite oxides for catalytic performance prediction. This work hence showcases a promising principle to design highly active perovskite catalysts suitable for oxidation reactions. Ministry of Education (MOE) Ministry of National Development (MND) National Environmental Agency (NEA) National Research Foundation (NRF) Accepted version This work is supported by the National Research Foundation, Prime Minister’s Office, Singapore, the Ministry of National Development, Singapore, and National Environment Agency, Ministry of the Environment and Water Resource, Singapore under the Closing the Waste Loop R&D Initiative as part of the Urban Solutions & Sustainability – Integration Fund (Award No. USS-IF-2019-4), and Singapore Ministry of Education [Tier 1, Grant number RG3/18(S); Tier 2, Grant number MOE2018-T2-2-027]. Authors thank the support from Environmental Chemistry and Materials Centre (ECMC) under Nanyang Environment and Water Research Institute (NEWRI), as well as the Sustainable Earth (SE) division of the Nanyang Technological University’s Interdisciplinary Graduate School (IGS). Technical supports from the Facility for Analysis, Characterization, Testing and Simulation (FACTS) in Nanyang Technological University for materials characterizations are acknowledged. Authors also appreciate the financial support from the Nanjing Tech University Research Start-up Fund [grant number 38274017111], and 111 Project (D18023).

Abstract Lithium–sulfur batteries (LSBs) are considered as the next generation of advanced rechargeable batteries because of their high energy density. In this study, sulfur and CoxS electrocatalyst are deposited on carbon nanotube buckypaper (S/CoxS/BP) by a facile electrodeposition method and are used as a binder-free high-performance cathode for LSBs. Elemental sulfur is deposited on buckypaper by electrooxidation of a polysulfide solution (~ S62−). This approach substantially increased the current and time efficiency of sulfur electrochemical deposition on conductive material for LSBs. S/CoxS/BP cathode could deliver an initial discharge capacity as high as 1650 mAh g−1 at 0.1 C, which is close to the theoretical capacity of sulfur. At current rate of 0.5 C, the S/CoxS/BP has a capacity of 1420 mAh g−1 at the first cycle and 715 mAh g−1 after 500 cycles with a fading rate of 0.099% per cycle. The high capacity of S/CoxS/BP is attributed to both the homogeneous dispersion of nanosized sulfur within BP and the presence of CoxS catalyst. The sodium dodecyl sulfate (SDS) pretreatment of BP renders it polarity to bind polysulfides and thus facilitates the good dispersibility of nanosized sulfur within BP. CoxS catalyst accelerates the kinetics of polysulfide conversion and reduces the presence of polysulfide in the cathode, which suppresses the polysulfide diffusion to anode, i.e., the shuttle effect. The mitigation of the active material loss improves not only the capacity but also the cyclability of S/CoxS/BP. Graphic Abstract

The optimization of microwave absorption is closely bound up with the of controllable strucuture of absorber materials. Hierarchically porous carbon (HPC) with two level pore structure has thriving as promising candidates for high performance microwave absorption application. However, fabricating HPC with tunable porous structure in a facile and sustainable manner with high yield is still a challenge for vast use in efficient electromagnetic (EM) wave absorption systems. Herein, a series of hierarchical porous carbon materials with different pore structures were synthesized from wheat flour dough through a facile biomass fermentation method. By gradually increasing the fermentation time, the conchoidal cavities gradually evolved to microscale macropore channels, and the number and size of pore increased synchronously. Microwave absorption studies revealed that the formation of macropore channels led to an apparent enhancement of dielectric properties, which can be further increased with the porosity increasing. Consequently, a strong absorption intensity of −52.0 dB at 2.50 mm and a broad microwave absorption bandwidth of 4.6 GHz at only 1.55 mm were achieved. Excellent microwave absorption performance can be ascribed to the improvement in dielectric loss. This approach shed the insights on achieving low-cost, green and industrial-scale production of EM absorber from renewable biomass.