Elaboration of Ni2P@C Composites with Hollow Porous Structure for Enhanced Overall Water Splitting

The electrocatalytic water splitting is greatly affected by overpotential, stability, and accessibility of active sites. Designing appropriate active components and tailoring their microstructure are crucial to improve electrocatalytic performance. Herein, using metal organic framework (MOF) as template, novel Ni2P@C composites are prepared as bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The best Ni2P@C-350 sample has a small onset overpotential (eta) of 57 mV, and up to 148 and 285 mV to afford 10 and 250 mA cm(-2) for HER. It only needs eta = 326 mV at 10 mA cm(-2) for OER, better than usual RuO2 electrode. Moreover, Ni2P@C-350||Ni2P@C-350 cell can work for overall water splitting more efficiently than common Pt/C||RuO2 cell, running stably within 30 h without obvious degradation. The excellent performance is attributed to its porous structure with easily accessible active sites, short ions transfer path, and superior structural stability, which enable a significant improvement on molecule level, e.g., the turnover frequency (TOF) of Ni2P@C-350 at eta = 250 mV is up to 0.84 s(-1), while that of pristine Ni2P is only 0.55 s(-1). These results highlight the effect of structure engineering, inspiring for electrode design of HER and OER.