Reconstruction of Copper Nanoparticles at Electrochemical CO₂ Reduction Reaction Conditions Occurs via Two‐step Dissolution/Redeposition Mechanism

Abstract

Copper is still the monometallic electrocatalyst of choice for electrochemical reduction of CO 2 (ERC) when added-value products, such as hydrocarbons and alcohols, are desired. However, severe morphological and structural changes are observed upon exposure to the ERC operation conditions. One of the pending questions in the community is what the mechanism behind this reconstruction is. In the present study, pulse-electrodeposited copper nanoparticles were exposed to different ERC relevant reductive potentials and tracked with identical location scanning electron microscopy (IL-SEM). This approach provides information on the morphological and structural history and subsequent change of Cu nanoparticles and with that a deep insight into the reconstruction events. With this evidence, we could interpret the observed structural changes as two separate electrochemical processes occurring one after another, namely copper dissolution from pre-oxidized native nanoparticles and subsequent (electro-) redeposition of the dissolved copper species in a form of new smaller Cu fragments.

Dynamic Evolution of Active Sites in Electrocatalytic CO2 Reduction Reaction: Fundamental Understanding and Recent Progress

“…[111] Taking a broader view, the morphology evolution form of Cu electrocatalysts is multiple, including deformation, corrosion, fragmentation, dissolution, redeposition, coalescence, Ostwald ripening, and so on. [27,32,130] The evolution behaviors are complicated when CO 2 adsorption, electrolyte, and applied voltage are considered. After the step of deformation or corrosion, the atoms detached from catalyst surface might directly dissolve into electrolyte.…”

Cu+ transient species mediate Cu catalyst reconstruction during CO2 electroreduction

“…At OCP the native surface oxides dissolve as Cu 2+ ions, this behavior is consistent with previous studies. [14][15][16] To simulate CO2RR conditions, a cathodic potential of -0.8 VRHE was applied between 5 min and 35 min. This is accompanied by a dramatic increase in the fluorescent signal which we assign to the release of Cu + ions from the catalyst and subsequent…”

“…Copper dissolves transiently during the formation of surface oxides and during oxide reduction to metallic copper. [14][15][16][17] As a result, Cu catalyst reconstruction is often associated with these redox processes. [14][15][16] These events occur at potentials close to the open circuit potential (OCP) of a typical CO2RR experiment, which is around +0.4VRHE (RHE = Reversible Hydrogen Electrode).…”

“…[14][15][16][17] As a result, Cu catalyst reconstruction is often associated with these redox processes. [14][15][16] These events occur at potentials close to the open circuit potential (OCP) of a typical CO2RR experiment, which is around +0.4VRHE (RHE = Reversible Hydrogen Electrode). 17 The catalyst typically encounters OCP during the cell assembly and electrolyte introduction or during a start/stop operation.…”

“…During the cell startup, where the working electrode experiences cathodic potentials, the redeposition of the Cu ions dissolved at OCP occurs and induces changes in the catalyst morphology and total exposed surface. [14][15][16] The OCP conditions can be avoided with an auxiliary cell controlling the cathode potential when the catalyst is introduced in the electrolyte or during a start-stop operation. In fact, the application of a cathodic potential during the cell assembly was proven essential to preserve the activity of Cu nanocatalysts smaller than 10 nm.…”