Integrating atomic scale catalyst design with transport engineering for stable and efficient CO2 electrolysis to CO in a membrane electrode assembly

Abstract

Electrochemical CO₂ reduction (CO₂R) offers a promising approach to for decarbonizing chemical manufacturing through production of carbon-neutral fuels. However, insufficient performance and instability of the membrane electrode assembly (MEA) reactors limit the commercial viability, with both metrics directly impacted by the CO₂R catalysts. Here we develop atomically dispersed nickel–nitrogen–carbon (NiNC) catalysts through a scalable synthesis approach that enables controlled dispersion of isolated Ni active sites using two different carbon supports. When using carbon nanotubes as a support, the resulting NiNCNT electrode achieves a partial current density towards CO of 558 mA cm⁻² with 92% faradaic efficiency towards CO at a cell voltage of 3.2 V and an energy efficiency of 39% at a total current density of 607 mA cm⁻². The MEA demonstrated stable operation at 100 mA cm⁻² over 210 hours, outperforming previously reported NiNC catalysts. Focused ion beam-scanning electron microscopy (FIB-SEM) tomography reveals the critical role of catalyst support architecture in governing electrode performance. COMSOL Multiphysics simulations using the 3D reconstructed images of the catalyst layers from FIB-SEM tomography demonstrated that the higher CO₂R performance of the NiNCNT electrode is due to improved CO₂ diffusion and a more uniform current-density distribution compared to the NiNCB electrode prepared with carbon black as the support. These results highlight the key role of catalyst-layer morphology in governing the CO₂R performance of the two catalysts, despite their similar Ni and N loadings. The stability and performance of the NiNCNT compared favourably to the state-of-the-art Ag-based catalysts, while bottom-up cost analysis estimated the projected purchase cost of the NiNCNT catalyst to be $589 USD per kg, substantially lower than $1900 USD per kg estimated for Ag-based catalysts, highlighting its potential for scalable and economically viable CO₂R electrolyzers.