Transition Metal Nitrides as Promising Catalyst Supports for Tuning CO/H₂ Syngas Production from Electrochemical CO₂ Reduction

The electrochemical carbon dioxide reduction reaction (CO₂ RR) to produce synthesis gas (syngas) with tunable CO/H₂ ratios has been studied by supporting Pd catalysts on transition metal nitride (TMN) substrates. Combining experimental measurements and density functional theory (DFT) calculations, Pd-modified niobium nitride (Pd/NbN) is found to generate much higher CO and H₂ partial current densities and greater CO Faradaic efficiency than Pd-modified vanadium nitride (Pd/VN) and commercial Pd/C catalysts. In-situ X-ray diffraction identifies the formation of PdH in Pd/NbN and Pd/C under CO₂ RR conditions, whereas the Pd in Pd/VN is not fully transformed into the active PdH phase. DFT calculations show that the stabilized *HOCO and weakened *CO intermediates on PdH/NbN are critical to achieving higher CO₂ RR activity. This work suggests that NbN is a promising substrate to modify Pd, resulting in an enhanced electrochemical conversion of CO₂ to syngas with a potential reduction in precious metal loading.