Direct conversion of captured forms of carbon, or reactive carbon capture (RCC), presents an opportunity to reduce the energy intensity and cost of direct CO2 utilization from dilute sources. While amine-based sorbents effectively capture CO2, their use for RCC presents numerous challenges with typical pure metal catalysts used for electrochemical CO2 reduction (CO2R). Here, using both theory and experiments, we find that Ni-N-C single atom catalysts are effective for RCC conversion to CO using a diethanolamine sorbent, in contrast to pure metal catalysts. Computational analysis reveals that RCC can proceed directly through direct reduction of the sorbent-CO2 adduct or indirectly by C-N bond breaking facilitating CO2 adsorption and subsequent reduction. We find that the latter mechanism is most prevalent at low overpotentials where we experimentally observe RCC selectivity. We also find experimentally that the rate of CO production for RCC with Ni-N-C catalysts can exceed pure bicarbonate solutions at intermediate sorbent concentration (0.1-0.5 M DEA) under dilute (10-25%) streams of CO2 at low overpotentials. The coordination environment of Ni sites and the solution speciation influence their RCC activity, with changes in protonation to coordinating N/C atoms resulting in changing the RCC mechanism and consequent activity. In situ X-ray absorption spectroscopy and computational analysis reveal restructuring under RCC conditions due to hydrogen coadsorption with DEA that limits the stability of Ni-N-C catalysts. This work highlights the importance of carefully controlling the catalyst and solution environment to achieve active and stable RCC electrocatalysis.
Ross et al. (Thu,) studied this question.