(A) study on synthesis and performance evaluation of metal chalcogenide, phosphide & carbon nanomaterials-based hybrid electrocatalysts

Abstract

Cost effective hydrogen evolution reaction (HER) catalyst without using precious metallic elements is a crucial demand for environment-benign energy production. In this thesis, two types of HER electrocatalysts, that is, amorphous molybdenum sulfide ($MoS_x$)/N-doped carbon nanotube (NCNT) forest hybrid and core-shell transition metal phosphosulfide/N-doped carbon nanotube (NCNT) hybrid were synthesized. Then, each of HER catalytic activity was evaluated. In the case of MoSx/NCNT hybrid, owing to the high wettability of N-doped graphitic surface and electrostatic attraction between thiomolybdate precursor anion and N-doped sites, ~2 nm-scale-thick amorphous $MoS_x$ layers were specifically deposited at NCNT surface under low temperature wet chemical process. The synergistic effect from the dense catalytic sites at amorphous $MoS_x$ surface and fluent charge transport along NCNT forest attains the excellent HER catalysis with onset overpotential as low as ~75 mV and small potential of 110 mV for $10 mA/cm^2$ current density, which demonstrates the successful activation of HER via synthesized hybrid. On the other hand, various core-shell transition metal phosphosulfide/NCNT hybrids synthesized through uniquely designed two-sept approach show prospective HER activity and stability. This is due to the positive influence of the nanoscale amorphous PS layer on activating hydrogen turnover. Also, the innovative hybridization of NCNT free standing electrodes with active materials paves the way for attaining such a noticeable catalytic performance. This demonstration offers a general rout to attain in-depth understanding of the structure-function relationships existed in the whole procedure of hydrogen evolution reaction.