Integrating Atomic Scale Catalyst Design with Transport Engineering for Stable and Efficient CO2 Electrolysis to CO in a Membrane Electrode Assembly

TL;DR

This study develops a scalable atomically dispersed Ni-NC catalyst supported on carbon nanotubes, achieving high efficiency, stability, and lower cost for CO2 electrolysis to CO in membrane electrode assemblies, advancing commercial viability.

Contribution

It introduces a scalable synthesis of Ni-NC catalysts supported on carbon nanotubes, demonstrating superior performance and stability in CO2 electrolysis compared to previous catalysts.

Findings

Achieved 558 mA cm-2 partial current density toward CO with 92% Faradaic efficiency.

Demonstrated stable operation over 210 hours at 100 mA cm-2.

Lower estimated cost of Ni-NCNT catalyst compared to Ag-based catalysts.

Abstract

Electrochemical CO2 reduction (CO2R) offers a promising approach to decarbonize chemical manufacturing through production of carbon-neutral fuels. However, insufficient performance and instability of membrane electrode assembly (MEA) reactors limit commercial viability, with both metrics directly impacted by the CO2R catalysts. Here we develop an atomically dispersed nickel-nitrogen-carbon (Ni-NC) catalyst through a scalable synthesis approach using two different carbon supports. When using carbon nanotubes as the support, the resulting Ni-NCNT electrode achieves a partial current density toward CO of 558 mA cm-2 with 92 percent Faradaic efficiency toward CO at a cell voltage of 3.2 V and an energy efficiency of 39 percent toward CO at a total current density of 607 mA cm-2. The MEA demonstrates stable operation at 100 mA cm-2 over 210 hours, outperforming previously reported Ni-NC catalysts. Focused ion beam scanning electron microscopy (FIB-SEM) tomography illustrates the key role of catalyst support on the performance of the electrode. COMSOL Multiphysics simulations using 3D reconstructed images of the catalyst layers from FIB-SEM tomography demonstrate that the higher CO2R performance of the Ni-NCNT electrode is due to improved CO2 diffusion and a more uniform current-density distribution compared to the Ni-NCB electrode prepared with carbon black as the support. The stability and performance of the Ni-NCNT compare favorably to state-of-the-art Ag-based catalysts, while bottom-up cost analysis estimates the purchase cost of the Ni-NCNT catalyst to be about 589 USD per kg, substantially lower than the 1900 USD per kg estimated for Ag-based catalysts.