Atomic-Layer-Deposited Pd/Cu2O/Cu Heterojunction as High-Efficiency Formate Catalysts and Boosting Aqueous Zn-CO2 Batteries

Abstract

The electrochemical reduction of carbon dioxide (CO₂RR) into value-added chemicals offers a sustainable pathway for mitigating greenhouse gas emissions and advancing carbon-neutral energy technologies. Among all possible CO₂RR products, formate/formic acid is particularly attractive due to its industrial relevance as a promising fuel for fuel cells and its high stability as an energy-storage medium. However, it remains challenging to obtain Cu-based catalysts with high selectivity and stability for CO₂ conversion to formate/formic acid. Herein, we report a metal Pd anchored onto a Cu₂O/Cu heterojunction (Pd-Cu₂O/Cu), synthesized via atomic layer deposition followed by electrochemical reduction. Structural and spectroscopic analyses confirmed the presence of Pd atoms, lattice defects, and abundant oxygen vacancies, which collectively modulated the electronic states and stabilized *OCHO intermediates while suppressing competing *H and *COOH pathways. Electrocatalytic tests of the Pd-Cu₂O/Cu in an H-type cell showed a remarkable formate Faradaic efficiency of 61.1% with a high partial current density of -24 mA cm⁻² at -0.9 V versus RHE. When integrated into an aqueous Zn-CO₂ battery, the catalyst outperformed most reported Cubased systems, achieving a maximum power density of 2.54 mW cm⁻² and stable cycling for 130 hours. Overall, this work demonstrates a cost-effective Zn-CO₂ battery technology, highlighting the practical potential of coupling CO₂ utilization with sustainable energy storage.