[Ni(PCy2NArginine2)2]2+ (CyArg) or [Ni(PCy2NBenzyl2)2]2+ (CyBn) were evaluated for H2 oxidation as a function of temperature, pressure, and solvent. 70 °C and 100 atm H2 result in a TOF of 1.1 × 106 s−1 and an overpotential of 240 mV for CyArg in water. In methanol the rates were 280 s−1 for CyArg and 80 s−1 for CyBn, demonstrating the importance of water and the outer coordination sphere (OCS).