Abstract
Replacement of precious platinum with efficient and low-cost catalysts for electrocatalytic hydrogen evolution at low overpotentials holds tremendous promise for clean energy devices. Here we report a novel type of robust cobalt–nitrogen/carbon catalyst for the hydrogen evolution reaction (HER) that is prepared by the pyrolysis of cobalt–N4 macrocycles or cobalt/o-phenylenediamine composites and using silica colloids as a hard template. We identify the well-dispersed molecular CoNx sites on the carbon support as the active sites responsible for the HER. The CoNx/C catalyst exhibits extremely high turnover frequencies per cobalt site in acids, for example, 0.39 and 6.5 s−1 at an overpotential of 100 and 200 mV, respectively, which are higher than those reported for other scalable non-precious metal HER catalysts. Our results suggest the great promise of developing new families of non-precious metal HER catalysts based on the controlled conversion of homogeneous metal complexes into solid-state carbon catalysts via economically scalable protocols.
Highlights
Replacement of precious platinum with efficient and low-cost catalysts for electrocatalytic hydrogen evolution at low overpotentials holds tremendous promise for clean energy devices
The CoNx/C catalysts are prepared by a straightforward pyrolysis process at high temperature in which cobalt–N4 macrocycles or cobalt/o-phenylenediamine composites are used as precursors and silica colloid is used as template
Three different precursors were examined in this work for the construction of the CoNx/C catalysts, including metal–N4 macrocycles, that is, cobalt tetramethoxyphenylporphyrin (CoTMPP) and vitamin V12 (VB12), as well as the cobalt/o-phenylenediamine composites (Co-oPD)
Summary
Replacement of precious platinum with efficient and low-cost catalysts for electrocatalytic hydrogen evolution at low overpotentials holds tremendous promise for clean energy devices. The CoNx/C catalyst exhibits extremely high turnover frequencies per cobalt site in acids, for example, 0.39 and 6.5 s À 1 at an overpotential of 100 and 200 mV, respectively, which are higher than those reported for other scalable non-precious metal HER catalysts. Independent efforts in solid-state electrocatalysis have led to several efficient inorganic crystalline catalysts, such as transition metal dichalcogenides[16,17,18,19,20,21,22,23,24], phosphides[25,26,27], carbides[28,29,30,31], nitrides[32,33], borides[28] and metallic nanoparticles embedded in carbon.[34,35] Despite their promising performance, it is highly challenging to control the atomic-scale surface structure of these inorganic materials and to preferentially expose a greater fraction of their active sites, for example, the edge sites of transition metal dichalcogenides[21,23]. The CoNx/C catalysts exhibit unprecedented TOFs (TOFs per Co atom of 0.39 and 6.5 s À 1 at an overpotential of 100 and 200 mV, respectively), which are superior to those of the recently reported breakthrough HER catalysts based on biomimetic molecules[14,15], metal dichalcogenides[18,21] and phosphides[25,26,27] (TOFo1.0 s À 1 at 200 mV overpotential)
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