Steering the structure and selectivity of CO2 electroreduction catalysts by potential pulses

Abstract

Convoluted selectivity trends and a missing link between reaction product distribution and catalyst properties hinder practical applications of the electrochemical CO2 reduction reaction (CO2RR) for multicarbon product generation. Here we employ operando X-ray absorption and X-ray diffraction methods with subsecond time resolution to unveil the surprising complexity of catalysts exposed to dynamic reaction conditions. We show that by using a pulsed reaction protocol consisting of alternating working and oxidizing potential periods that dynamically perturb catalysts derived from Cu2O nanocubes, one can decouple the effect of the ensemble of coexisting copper species on the product distribution. In particular, an optimized dynamic balance between oxidized and reduced copper surface species achieved within a narrow range of cathodic and anodic pulse durations resulted in a twofold increase in ethanol production compared with static CO2RR conditions. This work thus prepares the ground for steering catalyst selectivity through dynamically controlled structural and chemical transformations.

Probing the Dynamics of Low-Overpotential CO2-to-CO Activation on Copper Electrodes with Time-Resolved Raman Spectroscopy

“…Recent experimental and theoretical work has uncovered the importance of positively charged copper species (Cu + and Cu δ+ ) to tune the selectivity of copper electrocatalysts toward C 2 products. ,− These positively charged copper species are a result of alternating oxidation/reduction cycles in cyclic voltammetry (CV, anodic treatment) or pulsed electrolysis (PE) experiments. Moreover, lower CO2RR overpotentials were observed for copper oxide-derived catalysts ,− in PE experiments, − but the mechanism behind the increased selectivity and reduction of overpotential by positively charged copper species is still debated.…”

Reaction-Mediated Transformation of Working Catalysts

“…For instance, upon the modulation of excitation, 92 periodic perturbation of a catalytic system, along with phase-sensitive detection analysis, can minimize the noise, distinguish between the active and spectator species, and therefore allow the kinetic information to be extracted on active sites; potential pulse methods in electrocatalysis have demonstrated new possibilities for improving product selectivity over the traditional electrochemical operations. 93 A reaction-mediated dynamic transformation should emerge as another descriptor, in addition to the design and preparation of catalysts, to develop catalysis from a science into a sophisticated technology. This would enable scientific and technological innovations that are important for many applications, such as methane conversion, 94,95 plastic recycling, 96,97 and ammonia synthesis, 1 as well as a new era of photocatalysis 98 and plasma catalysis.…”

“…Catalyst operation under dynamic streams can help unravel and tailor the redox and structural transformations under the reaction conditions. For instance, upon the modulation of excitation, periodic perturbation of a catalytic system, along with phase-sensitive detection analysis, can minimize the noise, distinguish between the active and spectator species, and therefore allow the kinetic information to be extracted on active sites; potential pulse methods in electrocatalysis have demonstrated new possibilities for improving product selectivity over the traditional electrochemical operations . A reaction-mediated dynamic transformation should emerge as another descriptor, in addition to the design and preparation of catalysts, to develop catalysis from a science into a sophisticated technology.…”

Mechanistic Insights into Formation of CO and C2 Products in Electrochemical CO2 Reduction – the Role of the ECE Mechanism

“…16 Research endeavors to steer the reaction towards better C2 selectivity have provided new insights into the role of modifying the electrolyte and/or microenvironment, [17][18][19][20] catalyst faceting, [21][22] roughening the surface, [23][24] introducing mixed valence copper species, [25][26][27][28] nanostructuring the catalyst to introduce defects or to confine intermediates, [29][30][31] and pulsing the applied voltage. [32][33][34][35][36] Future endeavors to bring these advances to fruition stand to benefit from answers to outstanding questions about the fundamental mechanisms within the complex reaction network. Computational studies, in particular density functional theory (DFT) calculations of binding and activation energies, continue to provide detailed information into energetics and possible reaction pathways.…”