NiFe sulfide electronic structure modulation via metal doping towards enhanced urea oxidation reaction performance

Enhancement of urea oxidation reaction (UOR) activity of NiFe sulfide via metal doping, including V, Zn, Cr, Ag, and Ti, is demonstrated. X-ray photoelectron and absorption spectroscopy analyses show different degrees of electronic structure modulation of the Ni site due to the doping of the third metals having different t_2g and e_g occupancies. Cr reduces the energy needed for the in-situ formation of the oxyhydroxide, followed by Ti, V, and Ag. The reaction kinetics is accelerated by Ti, followed by Ag, Cr, and Zn. Ti also optimizes the d-band center and CO₂ adsorption energy, which is supported by density functional theory calculation. Self-reconstructed sulfate-containing oxyhydroxide during UOR is demonstrated via in-situ Raman and post-transmission electron microscopy analyses. The sulfate is also found to affect the potential required for the formation of the oxyhydroxide. The optimized NiFeTi-containing sulfide exhibits an excellent UOR potential of 1.36 V at 100 mA cm⁻² and is stable up to 80-h. This work provides a strategy and deep understanding in enhancing UOR performance of sulfide catalyst.