The electrochemical reduction of carbon dioxide (CO₂) provides a promising path towards the storage of renewable energy and to the sustainable synthesis of carbon-based chemical feedstocks. A key challenge for such a process is the low activity and selectivity of the CO₂ reduction reaction (CO₂RR). It is intensely desired to reduce CO₂ at low overpotentials, generating desired products at high current densities over extended periods, and reacting selectively without the formation of undesired byproducts. However, CO₂RR today is hindered by the low local concentration of CO₂ in aqueous electrolytes, in which more kinetically favorable reduction of protons to H₂ often outcompetes CO₂RR, eroding reaction selectivity. We developed a field-induced reagent concentration (FIRC) method to enhance the CO₂RR process. Through shaping electrodes into arrays of nanoneedles, we generated a high local electric field even when using low applied overpotentials. The high field concentrates electrolyte cations, and the cations bring with these a high local concentration of CO₂ to the active CO₂RR surface. Simulations revealed that 10-fold higher electric fields can be achieved on nanometrically sharp tips compared to that of quasi-planar regions. Utilizing bottom-up synthesized gold nanoneedle electrodes, record-low onset potential and record-high geometric current density at the low potential of −0.35 V with nearly quantitative (>95%) Faradaic efficiency (FE) for CO₂ reduction to CO conversion were achieved (1). This current density surpasses by an order of magnitude the performance of the best previously-reporeted gold nanorods, nanoparticles, and oxide-derived noble metal catalysts. The nanoneedle electrodes exhibited robust continuous reactions over 8 hours in an inorganic aqueous electrolyte. The FIRC concept has also be leveraged to build other metal nanoneedles and metal or metal sulfide covered gold nanoneedles. These electrodes exhibit much enhanced CO₂to hydrocarbon conversion efficiencies, proving the wider application of the FIRC concept.

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(1) M. Liu, Y. Pang, B. Zhang, P. D. Luna, O. Voznyy, J. Xu, X. Zheng, C. T. Dinh, F. Fan, C. Cao, F. P. Arquer, T. S. Safaei, A. Mepham, A. Klinkova, E. Kumacheva, T. Filleter, D. Sinton, S. O. Kelley, E. H. Sargent, Nature, 2016, 537, 382.