UCLA

Electrocatalytic reactive carbon capture (RCC), or the direct electroreduction of captured CO2-sorbent adducts, could enable more efficient conversion of dilute CO2 streams to value-added products. Amines are among the best sorbents for industrial carbon capture, but achieving efficient RCC with amines typically leads to low Faradaic efficiency for carbon based products in favor of the hydrogen evolution reaction (HER). HER is prevalent on account of equivalent formation of protonated amines, which promote HER, along with formation of the captured CO2-amine adduct. We employed a joint theory and experimental approach to demonstrate Ni-N-C single atom catalysts as effective catalysts for RCC conversion to CO. Computational analysis revealed that RCC can proceed through direct reduction of the CO2-sorbent adduct or via an indirect C-N bond breaking mechanism with an adsorbed CO2 intermediate. The prevalence of the mechanisms is potential dependent, with the indirect mechanism being predicted to be dominant at lower overpotentials where we experimentally observe CO selectivity. Electrochemical testing showed that intermediate concentrations of diethanolamine sorbent paired with dilute (10-25%) streams of CO2 results in superior selectivity to bicarbonate solutions under the same dilute CO2 conditions. Through in situ X-ray absorption spectroscopy and computational stability analysis, we found that RCC conditions can trigger restructuring and instability of Ni-N-C catalysts at higher overpotentials, leading to deactivation. Taken together, we find that controlling the coordination environment of the catalyst and the solution speciation are key to achieving active and stable RCC. This work was conducted under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (LLNL) under Contract DE-AC52-07NA27344. LLNL release number: LLNL-ABS-2014462.