Oxalate Catalytic Pathway Over Fault-Twinned PdRh Bimetallene Enables Ultrastable Mg-CO2 Batteries.

The reversibility of Mg-CO2 batteries relies on stabilizing the oxalate pathway, yet conventional catalysts, such as noble metal catalyst, transition metal catalyst, and redox mediator, tend to over-stabilize oxalate intermediates, impeding their desorption and leading to carbonate formation, challenging the stability of Mg-CO2 batteries. In this work, we propose a binding-weakening electronic modulation strategy that balances CO2 activation and MgC2O4 release for greatly enhancing the reversibility of Mg-CO2 batteries. We demonstrate that the fault-twinned PdRh bimetallene, where Rh incorporation downshifts the Pd d-band center for weakening oxalate adsorption and Rh-derived conduction states enhance CO2 activation, can well catalyze the reversible CO2 conversion. Meanwhile, strain fields from abundant stacking faults create undercoordinated Pd sites that facilitate CO2 → C2O4 2- conversion. This dual regulation stabilizes the oxalate pathway that previous catalysts could not sustain for achieving ultrastable cycling over 700 h with minimal polarization (1.10 V discharge, 1.21 V charge), which represents a benchmark for both durability and energy efficiency among Mg-CO2 batteries. The work establishes a new mechanistic foundation for rational pathway control in multivalent CO2 electrochemistry.