Zn-Based Catalysts for Selective and Stable Electrochemical CO₂Reduction at High Current Densities

Abstract

Practical electrochemical carbon dioxide (CO 2 ) reduction requires the development of selective and stable catalysts based on low-cost and Earth-abundant materials. In this work, we develop catalysts for CO 2 conversion to CO based on ZnO with various morphologies, including nanoparticles, nanorods, nanosheets, and random shapes. We found that ZnO nanorods exhibit the highest CO 2 to CO efficiency, with a high CO Faradaic efficiency (FE) of over 80% in a current density range of 50−160 mA cm 2 in both flow-cell and membrane electrode assembly (MEA) reactors. We found that the CO selectivity of ZnO-based catalysts slowly decreased over time at high current densities because of the depletion of the ZnO phase. We have developed an in-situ regeneration strategy for catalysts that involves periodic oxidations of the catalysts during electrochemical CO 2 reduction. Using this approach, we have demonstrated the conversion of CO 2 to CO with a stable CO FE of above 80% for 100 h at a current density of 160 mA cm −2 .

Exploring Heterostructures of D-Block Metal Oxides Coupled to ZnO for the Electrochemical Reduction of CO2

“…The partial HCOO – formation from the Co-ZnO GDEs is also responsible for hindering the production rate of CO ( j CO ). The ZnO GDE records a maximum j CO of −110 mA cm –2 , which agrees with the material’s already studied ECR performance . The Cu-ZnO catalyst records a maximum j CO of −120 mA cm –2 , indicating that Cu-ZnO is the most active for the ECR and especially for CO formation.…”

“…The ZnO GDE records a maximum j CO of −110 mA cm −2 , which agrees with the material's already studied ECR performance. 50 The Cu-ZnO catalyst records a maximum j CO of −120 mA cm −2 , indicating that Cu-ZnO is the most active for the ECR and especially for CO formation. As Wan et al described, 45 the material's performance is related to the ECR activity of both the Zn-phase in tandem catalyzing the ECR with the additional Cu-phase.…”

“…As described in our previous work, the catalyst ink preparation and the catalyst layer application were performed. 50 After preparation, the GDEs were placed in an oven at 120 °C for 1 h. This thermal treatment dries the electrode and eliminates any remaining surfactants originating from the ionomer suspension. Before any electrochemical measurements, the GDEs were soaked in a 1 M KOH solution to activate them chemically.…”

Progress and Perspectives of Pulse Electrolysis for Stable Electrochemical Carbon Dioxide Reduction

“…Numerous studies have demonstrated the effectiveness of pulse electrolysis in stabilizing the conversion of CO 2 to CO (Table ). For example, Stamatelos et al employed an in situ regeneration strategy on ZnO nanorods (ZnO NR) catalysts, which involves periodic oxidations during the electrochemical reduction of CO 2 . The ZnO catalysts undergo significant morphological and oxidation state changes during the ECR process because of the reduction of ZnO to metallic Zn and particle aggregation.…”

“…(b) Recovery of the ZnO-NR GDE performance by oxidation-CV cycles between −2 and 0.5 V strategy after FE deterioration caused by continuous ECR operation (at 160 mA cm –2 ). (c) Long-term operation of ECR at 160 mA cm 2 with periodic CV cycles between −2 and 1 V (CV2) every 1 h. Reproduced from ref . Copyright 2022 American Chemical Society.…”