NiP2 as an efficient non-noble metal cathode catalyst for enhanced hydrogen isotope separation in proton exchange membrane water electrolysis

Proton exchange membrane (PEM) water electrolysis is crucial for efficient hydrogen isotope separation (HIS) in liquid water. However, current cathode catalysts like platinum (Pt) suffer from scarcity and limited HIS performance. To overcome this challenge, we propose a simple and effective approach involving the synthesis of highly dispersed NiP2 nanoparticles supported on carbon (NiP2/C) through a solid-phase phosphidation reaction, and for the first time report its enhanced HIS performance as the cathode catalyst in PEM electrolyzer. The NiP2/C catalyst demonstrates excellent catalytic properties as a cathode catalyst for hydrogen evolution reaction (HER) in an acidic electrolyte, achieving low overpotential of only 157 mV at 10 mA/cm2 and Tafel slope of 95.6 mV/dec. Meticulous investigations and density functional theory (DFT) calculations reveal the intrinsic factors behind its performance. Furthermore, DFT calculations predict the HIS performance of both NiP2/C and Ni/C catalysts, revealing the advantages of NiP2/C over Ni/C. Experimental results obtained in practical PEM water electrolysis validate these predictions, as NiP2/C exhibits an impressive separation factor α of 6.36, nearly twice that of the Pt/C catalyst. Moreover, NiP2/C demonstrates reliable and consistent HIS performance during a 100-hour PEM electrolysis process. Importantly, our calculation model for deuterium enrichment in liquid water reveals that catalysts with higher separation factors α show faster deuterium enrichment and higher deuterium recovery rates. The utilization of NiP2/C as a non-noble metal cathode catalyst holds great promise for efficient and sustainable hydrogen isotope separation, addressing the limitations of precious metal catalysts and advancing clean energy technologies.