Thermally Engineered Sulfur Chemical State on Carbon Enables Bidirectional Tuning of Pd for Efficient Formic Acid Electrooxidation

The rational design of catalyst supports to achieve optimal metal-support interaction is critical for advancing Pd-based electrocatalysts for formic acid oxidation. Herein, we reported a thermally driven strategy to modulate the chemical state of sulfur on carbon support derived from propanethiol-functionalized carbon, which enabled bidirectional tuning of the Pd state and fundamentally altered the reaction pathway of formic acid oxidation. With an optimized calcination temperature of 700 °C, the Pd/SC-700 catalyst, featuring an exclusive thiophenic sulfur configuration, exhibited the strongest metal-support interaction, delivering an exceptional mass activity of 2222 mA mg–1 (8.3 times that of Pd/C), considerably superior stability (14 times that of Pd/C), and faster charge-transfer kinetics for formic acid oxidation. Gas chromatography analysis revealed a marked shift in reaction selectivity. Although CO remained the dominant product, its fraction dropped from 95.4% on Pd/C to 73.2% on Pd/SC-700, while the emergence of 7.2% CO2 directly confirmed activation of the direct dehydrogenation pathway. Kinetic analysis showed a linear j–v0.5 relationship (j = 0.62 + 0.204v0.5), indicating diffusion-controlled behavior with enhanced mass transport. This work provides a new strategy of thiol modification followed by thermal treatment that offers a simple yet scalable route to synthesize high-performance anode electrocatalysts for direct formic acid fuel cells.