Electrochemically-grown Chloride-free Cu2O nanocubes favorably electroreduce CO2 to Methane: The interplay of appropriate electrochemical protocol

Stefan Popović,Mohammed Azeezulla Nazrulla,Primož Šket,Khaja Mohaideen Kamal,Blaž Likozar,Luka Suhadolnik,Luka Pavko,Angelja Kjara Surca,Marjan Bele,Nejc Hodnik

doi:10.1016/j.electacta.2022.141458

Stefan Popović, Mohammed Azeezulla Nazrulla + Show 8 more

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https://doi.org/10.1016/j.electacta.2022.141458

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Abstract

Nowadays, electrochemical CO2 reduction reaction (CO2RR) to value-added products represents one of the major challenges in electrocatalysis. Copper-based nanocubes (Cu NCs) have been proposed as the front-runner's catalyst for the production of C2+ products at the industrial level. However, their selectivity (C1 vs. C2 product distribution) is rather complex depending on the dynamic structural transformations, the presence of mixed Cu+/Cu0 states, the microenvironment, and nanocatalyst-support interactions. Commonly, electrochemically-grown Cu NCs are prepared in the presence of chlorides that acts as a shaping agent. In this study, an optimized electrodeposition method for the synthesis of Cl−-free Cu2O nanocubes on a glassy carbon substrate with uniform size, shape, and loading is established. The successful preparation of chloride-free cuprous oxide nanocubes (Cu2O NCs) was confirmed with X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses. We report how the electrochemical double-layer capacitance (EDLC) method for electrochemical surface area (ECSA) determination with(out) subsequent return to the open-circuit potential (OCP) conditions before electrolysis influences the CO2RR activity/selectivity. When Cu2O NCs are subjected to the EDLC method (often considered a non-invasive method) and exposed to the OCP before electrolysis, they become active for methane (CH4) formation. Moreover, the influence of the potential window width (i.e. 200 and 400 mV) in which the EDLC-ECSA is employed and its correlations with the selectivity is presented. We underline the importance of the ECSA determination method and OCP on/off state as a triggering factor for reactivity/selectivity of particular Cu2O NCs for CO2RR and further emphasize the reconstructive nature of Cu2O NCs under CO2RR relevant conditions.

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