Enhancing the Performance of Ni-Mo Alkaline Hydrogen Evolution Electrocatalysts with Carbon Supports

Abstract

Alkaline water electrolysis offers the use of low-cost active materials and ancillary components, making it attractive for hydrogen production from renewables. Nevertheless, the practical performance of nonprecious electrocatalysts for alkaline hydrogen evolution still lags behind platinum-group metals. This disparity motivates work to understand how the solid-state chemistry of nonprecious transition metal alloys influences their activity toward alkaline hydrogen evolution. To this end, we have clarified the composition, chemical structure, and morphology of a previously reported Ni–Mo nanopowder electrocatalyst. The as-synthesized catalyst is mixed phase, comprising crystalline Ni-rich alloy nanoparticles embedded in a Mo-rich oxide matrix, and exhibits low activity toward hydrogen evolution. Its activity markedly increases upon activation by postdeposition reductive annealing or by including carbon black as a catalyst support. These results are consistent with a physical picture in which activity is limited not by kinetics but by electrical resistivity arising from thin oxide layers at the interfaces between the Ni–Mo alloy nanoparticles. Additional efforts to optimize the dispersion on carbon black supports resulted in mass activities exceeding 60 mA/mg (on the basis of Ni–Mo mass) at 100 mV overpotential. This was over 5-fold greater than we observed for activation by hydrogen annealing, and we postulate that it still represents a lower-bound estimate of the true activity of this catalyst.

Green hydrogen from anion exchange membrane water electrolysis: a review of recent developments in critical materials and operating conditions

“…34 Recently, a mixed phased catalyst, composed of crystalline Ni-rich Ni-Mo alloy nanoparticles embedded in a Mo-rich oxide matrix was prepared by Patel and co-workers. 35 This material has low activity toward hydrogen evolution. However, its activity markedly increased upon activation by postdeposition reductive annealing or by including carbon black as a catalyst support.…”

Structure Engineering of MoS2 via Simultaneous Oxygen and Phosphorus Incorporation for Improved Hydrogen Evolution

“…Up to now, a wide range of materials, including transition metal alloys, transition metal carbides, transition metal dichalcogenides, transition metal phosphides, and so on, has been studied as possible alternative HER electrocatalysts. Among them, molybdenum disulphide (MoS 2 ) has attracted great attention due to its unique crystal structure and properties .…”

Direct Observation of Ni–Mo Catalyst Formation via Thermal Reduction of Nickel Molybdate Nanorods

“…A catalyst mass loading of 50 µg/cm 2 was used throughout these measurements to minimize the confounding effects of electrical resistance associated with thicker films containing significant residual oxide. 25 The catalytic activity increased initially up to 400 • C and then decreased significantly at higher reduction temperatures. This trend is consistent with the TPR measurements, where two distinct chemical transformations were observed below and above 400 • C.…”

“…We recently reported that thermal reduction of compositionally homogeneous Ni-Mo oxide precursors results in spontaneous phase segregation into a core-shell nanocatalyst with excellent alkaline HER activity. 25 This result is intriguing for several reasons: first, the thermodynamically stable product under these treatment conditions is a single intermetallic with the empirical formula Mo 7 Ni 7 rather than the observed mixture containing a face-centered cubic (fcc) alloy and a mixed oxide. [26][27][28][29][30] Second, applying the same thermal reduction treatment to Mo oxide alone does not yield metallic Mo, but instead the sub-oxide MoO 3-δ .…”