Metal-N-Heterocyclic Carbene Porous Organic Polymers as Efficient Bifunctional Water-Splitting Electrocatalysts

The design and manufacture of bifunctional electrocatalysts are of great significance in the electrolysis of water. Herein, porous organic polymers (POPs) of metal-N-heterocyclic carbene were synthesized from imidazolium borate ionic POPs and supported on a nickel foam surface (Pd-NHC/NF, Ag-NHC/NF, and Cu-NHC/NF). Among them, Pd-NHC/NF exhibited high activity for both hydrogen evolution reaction and oxygen evolution reaction. The oxygen evolution overpotential of Pd-NHC/NF was 245 mV with a Tafel slope of 83 mV dec^-1; the hydrogen evolution overpotential was 139 mV with a Tafel slope of 94 mV dec^-1 at 10 mA cm^-2 in alkaline media. Additionally, the assembled Pd-NHC/NF||Pd-NHC/NF electrolyzer demonstrated excellent performance in electrocatalytic water-splitting, achieving a voltage of 1.55 V at 10 mA cm^-2 and showing outstanding stability for over 90 h in the long-term test. The results highlighted the substantial capability of Pd-NHC as a bifunctional catalyst for electrocatalytic water-splitting.