Electrochemical reduction of carbon dioxide (CO2) to carbon monoxide (CO) is the first step in the synthesis of more complex carbon-based fuels and feedstocks using renewable electricity1,2,3,4,5,6,7. Unfortunately, the reaction suffers from slow kinetics7,8 owing to the low local concentration of CO2 surrounding typical CO2 reduction reaction catalysts. Alkali metal cations are known to overcome this limitation through non-covalent interactions with adsorbed reagent species9,10, but the effect is restricted by the solubility of relevant salts. Large applied electrode potentials can also enhance CO2 adsorption11, but this comes at the cost of increased hydrogen (H2) evolution. Here we report that nanostructured electrodes produce, at low applied overpotentials, local high electric fields that concentrate electrolyte cations, which in turn leads to a high local concentration of CO2 close to the active CO2 reduction reaction surface. Simulations reveal tenfold higher electric fields associated with metallic nanometre-sized tips compared to quasi-planar electrode regions, and measurements using gold nanoneedles confirm a field-induced reagent concentration that enables the CO2 reduction reaction to proceed with a geometric current density for CO of 22 milliamperes per square centimetre at −0.35 volts (overpotential of 0.24 volts). This performance surpasses by an order of magnitude the performance of the best gold nanorods, nanoparticles and oxide-derived noble metal catalysts. Similarly designed palladium nanoneedle electrocatalysts produce formate with a Faradaic efficiency of more than 90 per cent and an unprecedented geometric current density for formate of 10 milliamperes per square centimetre at −0.2 volts, demonstrating the wider applicability of the field-induced reagent concentration concept.
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This work was supported by the Ontario Research Fund: Research Excellence programme, the Natural Sciences and Engineering Research Council (NSERC) of Canada, the CIFAR Bio-Inspired Solar Energy programme and a University of Toronto Connaught grant. B.Z. acknowledges funding from Shanghai Municipal Natural Science Foundation (14ZR1410200) and the National Natural Science Foundation of China (21503079). We thank X. Lan, P. Kanjanaboos, G. Walters, L. Levina, R. Wolowiec, D. Kopilovic, E. Palmiano, T. Burdyny and J. Tam from the University of Toronto for Au electron beam deposition, liquid products testing, AFM testing, TEM EELS measurements, discussions and additional aids during the course of study, Y. Tian from the King Abdullah University of Science and Technology for electrode preparation assistance, and M. Bajdich, L. D. Chen and K. Chan from Stanford University for advice on DFT calculations. This work has also benefited from the Spherical Grating Monochromator beamlines at the Canadian Light Source. DFT calculations were performed on the IBM BlueGene Q supercomputer with support from the Southern Ontario Smart Computing Innovation Platform (SOSCIP).
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Nature Chemistry (2019)