Deconvolution of phase-size-strain effects in metal carbide nanocrystals for enhanced hydrogen evolution

Understanding the descriptors of electrochemical activity and ways to modulate them are of paramount importance for the efficient structural engineering of electrocatalysts. Although, many studies separately elucidated the significance of thermodynamic and kinetic descriptors, lack of integrative approaches bars the potential utilization of these engineering tools for electrocatalytic activity enhancement. Here, through a facile post-carbonization synthetic technique using templated polyoxometalate based metal organic frameworks (POMOFs), we integrate three major structural engineering tools, viz. phase, size and strain into cost-effective Mo and W carbide electrocatalysts, and demonstrate how these factors qualitatively and quantitatively affect the critical descriptors of electrochemical activity. Deconvolution of these effects through combined experimental-theoretical analyses, shines new light on structure-activity relationships in this class of HER electrocatalysts. Optimum modulation of the structural tools culminated into the design of a superior electrocatalyst, consisting of ultrasmall γ-WC nanocrystals supported on N doped graphitic carbon that exhibited multifold activity enhancement in terms of onset potential, current density and Tafel slope compared to its structural analogues reported in this work and elsewhere. The present comprehensive study showcasing the effects of the structural engineering tools on activity will have considerable influence on future designs of more efficient nano-composite electrocatalysts.