Colloid synthesis of NiP/N, S-doped graphene as efficient bifunctional catalyst for alkaline hydrogen evolution and triiodide reduction reaction.

Designing high-efficient bifunction catalysts with excellent catalytic activity and enhanced charge-transfer capability in both alkaline hydrogen evolution reaction (HER) and triiodide reduction reaction (IRR) is of utmost significance to advance the development of green hydrogen production and photovoltaics, respectively, yet remains a crucial challenge. Here, highly dispersed and small-sized NiP nanocrystals with narrow size distribution was well attached on the surface of N, S co-doped graphene (NiP/NSG) by the facile hot-injection method. As expected, the optimized NiP/NSG requires a relatively low overpotential of 132.94 ± 0.08 mV to deliver a current density of 10 mA cm in alkaline condition, accompanied with remarkable long-time durability with negligible attenuation over 50 h. Density functional theory (DFT) calculations revealed that the positively synergic effect between NiP and NSG are in favor of modulating the rate determining step of the dissociation of HO to *(OH-H), thereby upgrading its HER activity. When used as the counter electrode catalyst for IRR in DSSCs, the resultant NiP/NSG exhibits extraordinary Pt-like catalytic activity and well electrochemical stability in iodide-based electrolyte, delivering a high photoelectric conversion performance (PCE) comparable to Pt. The improved PCE can be attributed to the accelerated interfacial charge-transfer capability around active sites for facilitating the reaction kinetics of IRR, as demonstrated by DFT calculations. This work provides an effective strategy for synthesizing cost-effective composites with multi-active sites and offering valuable insight into the structure-performance relationship, which is conducive to guide the synthesis of promising catalysts in the energy conversion field.