Small PdCx interstitial compound for efficient acidic CO2 electroreduction to formic acid

The development of efficient acidic CO₂ reduction reaction (CO₂RR) to high value-added chemical HCOOH at high current density (>1 A cm^-2) is crucial. However, addressing high potential, low Faradaic efficiency (FE), and poor stability simultaneously under acidic conditions remains challenging. Here, we construct small PdC_x interstitial compounds and engineer the interstitial atoms to modulate the catalyst's soft acid strength, thereby overcoming the triple challenge of "low overpotential-high current density-high stability" in acidic CO₂RR to HCOOH. Density functional theory (DFT) calculations and experimental characterization reveal that interstitial carbon infusion modulates Pd's soft acid strength and weakens the Pd-O bond energy to form and desorb HCOOH, circumventing CO poisoning of the catalyst. Meanwhile, interstitial carbon infusion optimizes electronic structures, enhancing OCHO intermediate coverage as well as the effective retention and utilization of *H. This effect suppresses hydrogen evolution reaction (HER) while enhancing HCOOH selectivity. The optimized PdC_0.13/CNT achieves >95% FE_HCOOH and demonstrates stability in a proton exchange membrane (PEM) electrolyzer, maintaining 1000 mA cm^-2 operation for 500 hours at 1.8 V cell voltage.