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1. Carbon aerogels with atomic dispersion of binary iron–cobalt sites as effective oxygen catalysts for flexible zinc–air batteries

   https://doi.org/10.1039/d0ta04633g  

   Chen, Yang ; Hu, Shengqiang ; Nichols, Forrest ; Bridges, Frank ; Kan, Shuting ; He, Ting ; Zhang, Yi ; Chen, Shaowei ( June 2020 , Journal of Materials Chemistry A)

   Iron single atom catalysts have emerged as one of the most active electrocatalysts towards the oxygen reduction reaction (ORR), but the unsatisfactory durability and limited activity for the oxygen evolution reaction (OER) has hampered their commercial applications in rechargeable metal–air batteries. By contrast, cobalt-based catalysts are known to afford excellent ORR stability and OER activity, due to the weak Fenton reaction and low OER Gibbs free energy. Herein, a bimetal hydrogel template is used to prepare carbon aerogels containing Fe–Co bimetal sites (NCAG/Fe–Co) as bifunctional electrocatalysts towards both ORR and OER, with enhanced activity and stability, as compared to the monometal counterparts. High-resolution transmission electron microscopy, elemental mapping and X-ray photoelectron spectroscopy measurements demonstrate homogeneous distributions of the metal centers within defected carbon lattices by coordination to nitrogen dopants. X-ray absorption spectroscopic measurements, in combination with other results, suggest the formation of FeN 3 and CoN 3 moieties on mutually orthogonal planes with a direct Fe–Co bonding interaction. Electrochemical measurements show that NCAG/Fe–Co delivers a small ORR/OER potential gap of only 0.64 V at the current density of 10 mA cm −2 , 60 mV lower than that (0.70 V) with commercial Pt/C and RuO 2 catalysts. When applied inmore »a flexible Zn–air battery, the dual-metal NCAG/Fe–Co catalyst also shows a remarkable performance, with a high open-circuit voltage of 1.47 V, a maximum power density of 117 mW cm −2 , as well as good rechargeability and flexibility. Results from this study may offer an ingenious protocol in the design and engineering of highly efficient and durable bifunctional electrocatalysts based on dual metal-doped carbons.« less
2. Scalable, highly stable Si-based metal-insulator-semiconductor photoanodes for water oxidation fabricated using thin-film reactions and electrodeposition

   https://doi.org/10.1038/s41467-021-24229-y  

   Lee, Soonil ; Ji, Li ; De Palma, Alex C. ; Yu, Edward T. ( June 2021 , Nature Communications)

   Metal-insulator-semiconductor (MIS) structures are widely used in Si-based solar water-splitting photoelectrodes to protect the Si layer from corrosion. Typically, there is a tradeoff between efficiency and stability when optimizing insulator thickness. Moreover, lithographic patterning is often required for fabricating MIS photoelectrodes. In this study, we demonstrate improved Si-based MIS photoanodes with thick insulating layers fabricated using thin-film reactions to create localized conduction paths through the insulator and electrodeposition to form metal catalyst islands. These fabrication approaches are low-cost and highly scalable, and yield MIS photoanodes with low onset potential, high saturation current density, and excellent stability. By combining this approach with a p⁺n-Si buried junction, further improved oxygen evolution reaction (OER) performance is achieved with an onset potential of 0.7 V versus reversible hydrogen electrode (RHE) and saturation current density of 32 mA/cm²under simulated AM1.5G illumination. Moreover, in stability testing in 1 M KOH aqueous solution, a constant photocurrent density of ~22 mA/cm²is maintained at 1.3 V versus RHE for 7 days.
3. Water oxidation kinetics of nanoporous BiVO ₄ photoanodes functionalised with nickel/iron oxyhydroxide electrocatalysts

   https://doi.org/10.1039/d0sc06429g  

   Francàs, Laia ; Selim, Shababa ; Corby, Sacha ; Lee, Dongho ; Mesa, Camilo A. ; Pastor, Ernest ; Choi, Kyoung-Shin ; Durrant, James R. ( June 2021 , Chemical Science)

   In this work, spectroelectrochemical techniques are employed to analyse the catalytic water oxidation performance of a series of three nickel/iron oxyhydroxide electrocatalysts deposited on FTO and BiVO 4 , at neutral pH. Similar electrochemical water oxidation performance is observed for each of the FeOOH, Ni(Fe)OOH and FeOOHNiOOH electrocatalysts studied, which is found to result from a balance between degree of charge accumulation and rate of water oxidation. Once added onto BiVO 4 photoanodes, a large enhancement in the water oxidation photoelectrochemical performance is observed in comparison to the un-modified BiVO 4 . To understand the origin of this enhancement, the films were evaluated through time-resolved optical spectroscopic techniques, allowing comparisons between electrochemical and photoelectrochemical water oxidation. For all three catalysts, fast hole transfer from BiVO 4 to the catalyst is observed in the transient absorption data. Using operando photoinduced absorption measurements, we find that water oxidation is driven by oxidised states within the catalyst layer, following hole transfer from BiVO 4 . This charge transfer is correlated with a suppression of recombination losses which result in remarkably enhanced water oxidation performance relative to un-modified BiVO 4 . Moreover, despite similar electrocatalytic behaviour of all three electrocatalysts, we show that variationsmore »in water oxidation performance observed among the BiVO 4 /MOOH photoanodes stem from differences in photoelectrochemical and electrochemical charge accumulation in the catalyst layers. Under illumination, the amount of accumulated charge in the catalyst is driven by the injection of photogenerated holes from BiVO 4 , which is further affected by the recombination loss at the BiVO 4 /MOOH interface, and thus leads to deviations from their behaviour as standalone electrocatalysts.« less
4. Atomically dispersed Fe–N–C decorated with Pt-alloy core–shell nanoparticles for improved activity and durability towards oxygen reduction

   https://doi.org/10.1039/d0ee00832j  

   Ao, Xiang ; Zhang, Wei ; Zhao, Bote ; Ding, Yong ; Nam, Gyutae ; Soule, Luke ; Abdelhafiz, Ali ; Wang, Chundong ; Liu, Meilin ( September 2020 , Energy & Environmental Science)

   One of the key challenges that hinders broad commercialization of proton exchange membrane fuel cells is the high cost and inadequate performance of the catalysts for the oxygen reduction reaction (ORR). Here we report a composite ORR catalyst consisting of ordered intermetallic Pt-alloy nanoparticles attached to an N-doped carbon substrate with atomically dispersed Fe–N–C sites, demonstrating substantially enhanced catalytic activity and durability, achieving a half-wave potential of 0.923 V ( vs.  RHE) and negligible activity loss after 5000 cycles of an accelerated durability test. The composite catalyst is prepared by deposition of Pt nanoparticles on an N-doped carbon substrate with atomically dispersed Fe–N–C sites derived from a metal–organic framework and subsequent thermal treatment. The latter results in the formation of core–shell structured Pt-alloy nanoparticles with ordered intermetallic Pt 3 M (M = Fe and Zn) as the core and Pt atoms on the shell surface, which is beneficial to both the ORR activity and stability. The presence of Fe in the porous Fe–N–C substrate not only provides more active sites for the ORR but also effectively enhances the durability of the composite catalyst. The observed enhancement in performance is attributed mainly to the unique structure of the composite catalyst, asmore »confirmed by experimental measurements and computational analyses. Furthermore, a fuel cell constructed using the as-developed ORR catalyst demonstrates a peak power density of 1.31 W cm −2 . The strategy developed in this work is applicable to the development of composite catalysts for other electrocatalytic reactions.« less
5. Discovery of LaAlO3 as an efficient catalyst for two-electron water electrolysis towards hydrogen peroxide

   https://doi.org/10.1038/s41467-022-34884-4  

   Baek, Jihyun ; Jin, Qiu ; Johnson, Nathan Scott ; Jiang, Yue ; Ning, Rui ; Mehta, Apurva ; Siahrostami, Samira ; Zheng, Xiaolin ( November 2022 , Nature Communications)

   Electrochemical two-electron water oxidation reaction (2e-WOR) has drawn significant attention as a promising process to achieve the continuous on-site production of hydrogen peroxide (H₂O₂). However, compared to the cathodic H₂O₂generation, the anodic 2e-WOR is more challenging to establish catalysts due to the severe oxidizing environment. In this study, we combine density functional theory (DFT) calculations with experiments to discover a stable and efficient perovskite catalyst for the anodic 2e-WOR. Our theoretical screening efforts identify LaAlO₃perovskite as a stable, active, and selective candidate for catalyzing 2e-WOR. Our experimental results verify that LaAlO₃achieves an overpotential of 510 mV at 10 mA cm⁻²in 4 M K₂CO₃/KHCO₃, lower than those of many reported metal oxide catalysts. In addition, LaAlO₃maintains a stable H₂O₂Faradaic efficiency with only a 3% decrease after 3 h at 2.7 V vs. RHE. This computation-experiment synergistic approach introduces another effective direction to discover promising catalysts for the harsh anodic 2e-WOR towards H₂O₂.