Xueqin Zhang

Bio: Xueqin Zhang is an academic researcher from University of Queensland. The author has contributed to research in topics: Anaerobic oxidation of methane & Anode. The author has an hindex of 10, co-authored 31 publications receiving 382 citations. Previous affiliations of Xueqin Zhang include Zhejiang Gongshang University.

Gas diffusion electrodes (GDEs) for electrochemical reduction of carbon dioxide, carbon monoxide, and dinitrogen to value-added products: a review

Abstract: Electrochemical reduction of gaseous feeds such as CO2, CO, and N2 holds promise for sustainable energy and chemical production. Practical application of this technology is impeded by slow mass transport of the sparingly soluble gases to conventional planar electrodes. Gas diffusion electrodes (GDEs) maintain a high gas concentration in the vicinity of the catalyst and improve mass transport, thereby resulting in current densities higher by orders of magnitude. However, gaseous feeds cause changes to the GDE environment, and specific features are required to efficiently tune the product selectivity and improve reaction stability. Herein, with a comprehensive review of the challenges and advances in GDE development for various electrocatalytic reactions, we intend to complement the body of material-focused reviews. This review outlines GDE fundamentals and highlights key advantages of GDE over conventional electrodes. Through critical discussion about steps in GDE fabrication, and specific shortcomings and remedial strategies for various electrochemical applications, this review discusses connections, unique design criteria, and potential opportunities for gas-fed reactions and desired products. Finally, priorities for future studies are suggested, to support the advancement and scale-up of GDE-based electrochemical technologies.

Biochar-mediated anaerobic oxidation of methane

Abstract: Biochar was recently identified as an effective soil amendment for CH4 capture. Corresponding mechanisms are currently recognized to be from physical properties of biochar, providing a favorable growth environment for aerobic methanotrophs which perform aerobic methane (CH4) oxidation. However, our study shows that the chemical reactivity of biochar can also stimulate anaerobic oxidation of CH4 (AOM) by anaerobic methanotrophic archaea (ANME) of ANME-2d, which proposes another plausible mechanism for CH4 mitigation by biochar amendment in anaerobic environments. It was found that, by adding biochar as the sole electron acceptor in an anaerobic environment, CH4 was biologically oxidized, with CO2 production of 106.3 ± 5.1 μmol g-1 biochar. In contrast, limited CO2 production was observed with chemically reduced biochar amendment. This biological nature of the process was confirmed by mcr gene transcript abundance as well as sustained dominance of ANME-2d in the microbial community during microbial incubations with active biochar amendment. Combined FTIR and XPS analyses demonstrated that the redox activity of biochar is related to its oxygen-based functional groups. On the basis of microbial community evolution as well as intermediate production during incubation, different pathways in terms of direct or indirect interactions between ANME-2d and biochar were proposed for biochar-mediated AOM.

Shape-tuned electrodeposition of bismuth-based nanosheets on flow-through hollow fiber gas diffusion electrode for high-efficiency CO2 reduction to formate

Abstract: Gas-phase CO2 electrochemical reduction reaction (CO2RR) requires advanced gas diffusion electrodes (GDEs) for efficient mass transport. Meantime, engineering catalyst nanostructure and tuning surface wettability are decisive to enhance three-phase interfaces formation. Herein, Bi-based nanosheets are uniformly grown on flow-through Cu hollow fiber GDE (HFGDE) to benefit from the unique shape of HFGDEs, and abundant active surface area of nanosheets. Pulse electrodeposition is used to replenish Bi3+ ions in the vicinity of HFGDEs for uniform growth of Bi nanosheets. Further, thermal oxidation of nanosheets not only maximized the active sites and improved surface wettability but also induced Bi/Bi2O3 junctions in nanosheets, enhancing formate production via switching the rate-limiting step from the initial electron transfer to hydrogenation. Consequently, a current density of 141 mA cm−2 at -1 V vs. RHE with formate faradaic efficiency of 85 % and over six times greater catalyst mass activity compared to bulk particle shaped Bi, were achieved, outperforming other reported Bi-based GDEs used for formate production in bicarbonate electrolytes. This comes from less charge-transfer resistance, higher surface roughness, and improved wettability of Bi nanosheets after oxidation. This work represents a facile strategy to engineer efficient HFGDEs as advanced electrode materials for similar electrochemical reactions with low aqueous solubility gas-phase feeds.

Tuning the Product Selectivity of the Cu Hollow Fiber Gas Diffusion Electrode for Efficient CO2 Reduction to Formate by Controlled Surface Sn Electrodeposition.

Abstract: The efficient CO2 electrochemical reduction reaction (CO2RR) relies not only on the development of selective/active catalysts but also on the advanced electrode configuration to solve the critical issue of poor CO2 mass transport and derived sluggish cathodic reaction kinetics. In this work, to achieve a favorable reaction rate and product selectivity, we designed and synthesized an asymmetric porous Cu hollow fiber gas diffusion electrode (HFGDE) with controlled Sn surface electrodeposition. The HFGDE derived from the optimal Sn electrodeposition condition exhibited a formate Faradaic efficiency (FE) of 78% and a current density of 88 mA cm-2 at -1.2 V versus reversible hydrogen electrode, which are more than 2 times higher than those from the pristine Cu HFGDE. The achieved performance outperformed most of the other Sn-based GDEs, indicating the creation of sufficient contact among CO2, electrolyte, and electrode catalyst through the design of the hollow fiber pore structure and catalytic active sites. The enhancement of formate production selectivity and the suppression of the hydrogen by-product were attributed to the optimized ratio of SnOx species on the electrode surface. The best performance was seen in the HFGDE with the highest Sn2+/Sn4+ (120 s deposition), likely due to the modulating effect of the Cu substrate via electron donation with Sn species. The selectivity control strategy developed in the asymmetric HFGDE provides an efficient and facile method to stimulate selective electrochemical reactions in which the gas-phase reactant with low solubility is involved.

Rational Catalyst and Electrolyte Design for Co2 Electroreduction Towards Multicarbon Products

Abstract: CO2 electroreduction reaction (CO2RR) to fuels and feedstocks is an attractive route to close the anthropogenic carbon cycle and store renewable energy. The generation of more reduced chemicals, especially multicarbon oxygenate and hydrocarbon products (C2+) with higher energy density is highly desirable for industrial applications. However, selective conversion of CO2 to C2+ suffers from high overpotential, low reaction rate and low selectivity, and the process is extremely sensitive to the catalyst structure and electrolyte. Here we discuss strategies to achieve high C2+ selectivity through rational design of the catalyst and electrolyte. Current state-of-the-art catalysts, including Cu and Cu-bimetallic catalysts as well as alternative materials are considered. The importance of taking into consideration the dynamic evolution of the catalyst structure and composition are highlighted, focusing on findings extracted from in situ and operando characterizations. Additional theoretical insight into the reaction mechanisms underlying the improved C2+ selectivity of specific catalyst geometries/compositions in synergy with a well-chosen electrolyte are also provided.

Gas diffusion electrodes (GDEs) for electrochemical reduction of carbon dioxide, carbon monoxide, and dinitrogen to value-added products: a review

Abstract: Electrochemical reduction of gaseous feeds such as CO2, CO, and N2 holds promise for sustainable energy and chemical production. Practical application of this technology is impeded by slow mass transport of the sparingly soluble gases to conventional planar electrodes. Gas diffusion electrodes (GDEs) maintain a high gas concentration in the vicinity of the catalyst and improve mass transport, thereby resulting in current densities higher by orders of magnitude. However, gaseous feeds cause changes to the GDE environment, and specific features are required to efficiently tune the product selectivity and improve reaction stability. Herein, with a comprehensive review of the challenges and advances in GDE development for various electrocatalytic reactions, we intend to complement the body of material-focused reviews. This review outlines GDE fundamentals and highlights key advantages of GDE over conventional electrodes. Through critical discussion about steps in GDE fabrication, and specific shortcomings and remedial strategies for various electrochemical applications, this review discusses connections, unique design criteria, and potential opportunities for gas-fed reactions and desired products. Finally, priorities for future studies are suggested, to support the advancement and scale-up of GDE-based electrochemical technologies.

Hydrochar-Facilitated Anaerobic Digestion: Evidence for Direct Interspecies Electron Transfer Mediated through Surface Oxygen-Containing Functional Groups.

Abstract: Acceleration of the anaerobic digestion (AD) process is crucial to achieving energy-efficient recycling of organic wastes. Hydrochar is produced by hydrothermal liquefaction of biomass, yet its application in the AD process is rarely reported. The present study showed that sewage sludge-derived hydrochar (SH) enhanced the methane production rate of glucose by 37%. SH increased the methane production rate from acetate but did not affect acidification and the methane production rate from H2/CO2. SH enhanced hydrogenotrophic methanogenesis, which could be due to direct interspecies electron transfer (DIET) by converting H+, e-, and CO2 to methane. Trichococcus and Methanosaeta were dominant in the AD process with SH. Label-free proteomic analysis showed Methanosaeta was involved in DIET as reflected by the up-regulation of proteins involved in hydrogenotrophic methanogenesis. Hydrochars derived from corn straw (CH), Enteromorpha algae (EH), and poplar wood (PH), as well as activated carbon (AC), were also tested in the AD process. SH, CH, and EH obviously increased the methane production rates, which were 39%, 15%, and 20% higher than the control experiment, respectively. It was neither electrical conductivity nor the total redox property of hydrochars and AC but the abundances of surface oxygen-containing functional groups that correlated to the methane production rates.