MoS2/carbon heterostructured catalysts for the hydrogen evolution reaction: N-doping modulation of substrate effects in acid and alkaline electrolytes

Carbon-supported MoS2 is a promising electrocatalyst for hydrogen evolution reaction (HER), however, it is not well understood how carbon substrate effects might modulate MoS2 activity. Herein, we report on development and characterization of heterostructured thin-film electrodes consisting of MoS2 supported on nitrogenated graphitic carbons, that display well defined geometry, morphology and concentration of N-functionalities. Carbon supports were synthesized via magnetron sputtering and thermal modifications, yielding graphitized smooth thin-films rich in either pyridinic-N or graphitic-N functionalities. CVD deposition of MoS2 using close proximity precursor methods yielded MoS2/carbon electrodes with high contact area between the two phases, thus enabling investigation of substrate effects on MoS2 activity. Voltammetry in acid and alkaline electrolytes indicates that N-functionalities affect HER performance with effects being pH-dependent. At low pH, similar overpotentials and Tafel slopes are observed independently of whether graphitic-N or pyridinic-N groups are present at the carbon support. However, at high pH, pyridinic-N groups lead to suppression of HER activity. We propose that deprotonation and lone-pair availability at pyridinic-N modulate activity with electrostatic interactions leading to weaker MoS2-carbon coupling for the deprotonated form. This has important implications for smart design of heterostructured electrocatalysts where synergistic/inhibitory behaviors might be exploited/avoided to control performance in HER electrocatalysis.