Reaction Parameters Influencing Cobalt Hydride Formation Kinetics: Implications for Benchmarking H₂-Evolution Catalysts

Abstract

The need for benchmarking hydrogen evolution catalysts has increasingly been recognized. The influence of acid choice on activity is often reduced to the overpotential for catalysis. Through the study of a stable cobalt hydride complex, we demonstrate the influence of acid choice, beyond pK_a, on the kinetics of hydride formation. A linear free energy relationship between acid pK_a and second-order rate constants is observed for weaker acids. For stronger acids, however, further increases in pK_a do not correlate to increases in rate constants. Further, steric bulk around the acidic proton is shown to influence rate constants dramatically. Together, these observations reveal the complex factors dictating catalyst performance.