CO₂ electrolysis (CO₂E) powered by renewable electricity offers a sustainable route for fuel and chemical production while reducing CO₂ emissions. Traditionally, CO₂E is coupled with the oxygen evolution reaction (OER) at the anode, but OER suffers from high overpotentials, slow kinetics, and low-value oxygen production, reducing overall efficiency. To address this, alternative anodic reactions, such as the hydrogen oxidation reaction (HOR), have been explored.¹ HOR has been widely studied in fuel cell applications and for electrochemical hydrogen pumps (EHP) to produce high purity hydrogen streams from an impure hydrogen input at the anode.²

In this work, we leverage the EHP concept and integrate it with CO₂ electrolysis to reduce overall cell voltage and simplify electrolyzer operation. Owing to the fast kinetics and low overpotential of HOR, we demonstrate a substantial decrease in cell voltage, enabling industrially relevant current densities of up to 500 mAcm^-2 at < 2 V without the need for a circulating aqueous electrolyte.

We systematically investigate HOR-coupled CO₂ electrolysis and evaluate key factors affecting its efficiency and scalability. Using a membrane electrode assembly (MEA) configuration, we first establish the feasibility of electrochemical hydrogen pumping, coupling HOR at the anode with the hydrogen evolution reaction (HER) at the cathode. In this configuration, current densities of 500 mA cm⁻² were sustained at cell voltages below 0.5 V. We then replace HER with CO₂ electroreduction at the cathode, employing silver and platinum as the cathode and anode catalysts, respectively. The performance of both proton exchange membranes (PEMs) and anion exchange membranes (AEMs) is systematically compared, followed by an investigation of the role of alkali metal cations in this architecture.

Furthermore, operando wide-angle X-ray scattering (WAXS) and X-ray fluorescence (XRF) measurements reveal important insights into cation transport, local cation accumulation, and water management within the cell. These observations provide a deeper understanding of systems involving gaseous reactants at both electrodes and highlight critical transport phenomena governing device performance. Overall, our findings demonstrate that HOR-coupled CO₂ electrolysis can significantly improve energy efficiency and offer a promising route toward scalable and economically viable carbon utilization technologies.