Abstract
The effect of the nature of the transition metal on the structure and activity for hydrogen evolution of Metal-N-C catalysts synthesized via the pyrolysis of metal salts and a Zn-based metal organic framework was investigated. It is found that W, Mo, Cu and Zn lead to amorphous carbons with high specific area while Cr, Mn, Fe, Co and Ni lead to more graphitic carbons with a lower specific area. Metal salts with a high redox potential are fully reduced during pyrolysis while others are only partially reduced. Electrochemical activity toward hydrogen evolution was investigated at pH 1 and pH 13. Hydrogen evolution on these Metal-N-C catalysts is generally more facile at pH 1 than at pH 13, paralleling the trends observed for noble metal surfaces. The Co-, Ni-and Fe-N-C catalysts are the most active at pH 13 while CoN -C and Cr-N-C are the most active at pH 1. The activity of the latter catalysts stems from metallic cobalt particles encapsulated in carbon and from a chromium carbo-nitride phase, respectively.