(544bp) Addressing Electronic Conductivity Limitations in Non-Precious Metal Alloy Electrocatalysts

Membrane-based alkaline electrolyzers are promising for cost-effective production of hydrogen from renewables. The non-corrosive environment provided by these electrolyzers enable the use of earth abundant, non-precious transition metal electrocatalysts. While Ni and Ni-based composites have been used for many years for the alkaline hydrogen and oxygen evolution reaction (HER and OER, respectively), their practical performance still lags considerably behind noble metals operating in acid. We are therefore studying composition-structure-activity relationships in Ni-based hydrogen evolution electrocatalysts with the ultimate goal of validating their use in efficient alkaline anion exchange membrane (AAEM) electrolyzer systems.

Prior approaches for synthesis and processing of highly active Ni–Mo HER electrocatalysts relied on electrodeposition or thermal reduction of catalyst precursors directly on conducting substrates [1,2]. By contrast, deposition of unsupported Ni–Mo nanopowders on Ni or Ti substrates yields very low HER performance unless the deposition is followed by a thermal annealing step in a reducing environment [3]. We have now shown that this thermal annealing step can be eliminated by incorporating carbon black into the Ni–Mo nanopowder precursor mixture. Further studies of catalyst composition, morphology, and carbon loading give clear evidence that the advantageous role of carbon is to improve electrical conductivity, which is otherwise limited by the spontaneous formation of resistive surface oxides on Ni–Mo nanoparticles upon handling in air. Moreover, well-mixed Ni–Mo/C composites yield HER specific activity (normalized to Ni–Mo mass) that is several times greater than carbon-free catalysts prepared under otherwise identical conditions. These catalyst composites can be processed into coatings in the same way as commercial Pt/C, thereby providing a pathway to use nonprecious catalysts as drop-in replacements for noble metals in AAEM electrolyzers.

References:

[1] I. A. Raj and K. I. Vasu, “Transition metal-based hydrogen electrodes in alkaline solution - electrocatalysis on nickel based binary alloy coatings,” J. Appl. Electrochem., vol. 20, no. 1, pp. 32–38, Jan. 1990.

[2] D. E. Brown, M. N. Mahmood, M. C. M. Man, and A. K. Turner, “Preparation and characterization of low cvervoltage tranistion metal alloy electro-catalysts for hydrogen evolution in alkaline solutions, Electrochemica Acta, vol. 29, no. 11, pp. 1551-1586, 1984”

[3] J. R. McKone, B. F. Sadtler, C. A. Werlang, N. S. Lewis, and H. B. Gray, “Ni-Mo nanopowders for efficient electrochemical hydrogen evolution,” ACS Catal., 2013.