Anticipated increases in worldwide energy consumption, the reality of ultimately limited hydrocarbon fuels, as well as their contribution to global warming, have all encouraged the development and commercialization of renewable, carbon neutral, energy technologies. An issue for renewable energy sources like solar, wind and wave energy is their intermittency. An efficient means to overcome this intermittency is to build excess capacity into the generating plants and to use that excess capacity to produce high energy density hydrogen fuel via water electrolysis for on demand reconversion to electrical energy in fuel cells. A major impediment to this solution is that commercial water splitting electrolyzers use scarce and costly precious metal catalysts which make such an energy storage/recovery scheme prohibitively expensive. Alternative, earth-abundant, non-precious metal catalysts are highly desired.

We recently demonstrated that purified single wall carbon nanotubes (SWNT), and select layered graphitic materials, activated by a simple electrochemical process, provide an exceptional non-precious metal electrocatalyst for the hydrogen evolution and the hydrogen oxidation reactions in both acidic and near neutral pH. [1] Here we validate this result for hydrogen evolution in a single-cell PEM electrolyzer. The MEAs studied used Nafion 115 and an IrRuO_x anode. Three distinct cathodes were tested: 1) commercially available Pt loaded (3.0 mg/cm²) Vulcan X-72 carbon (for a point of comparison); 2) non-activated SWNTs; and 3) activated SWNTs. In all cases I-V measurements were performed at 80^oC. The commercial Pt loaded MEA exhibited the high gas production rates expected from engineered Pt, converting 1.0 A/cm² at 1.67 V. The non-activated SWNTs yielded very low gas production rates requiring 1.89 V for a current of only 0.040 A/cm². The activated SWNTs demonstrated a performance completely comparable, at all potentials, with that of the commercial Pt electrode (see Figure), attaining 1.0 A/cm² at 1.64 V. Ninety hours of operation showed no degradation in the cathode performance.

It has been estimated that a 50% reduction in the cathode Pt used would result in a 15% electrolyzer cost reduction. [2] Our entirely Pt–free electrode using only earth abundant carbon could nearly double that cost saving.

Acknowledgements.

This work was supported by Nanoholdings, LLC.

References:

[1] R. K. Das, Y. Wang, S. V. Vasilyeva, E. Donoghue, I. Pucher, G. Kamenov, H.-P. Cheng, A. G. Rinzler, ACS Nano, 8 (8), 8447–8456 (2014)

[2] K. E. Ayers, E. B. Anderson, C. B. Capuano, B. D. Carter, L. T. Dalton, G. Hanlon, J. Manco, and M. Niedzwiecki, ECS Transactions, 33 (1), 3-15 (2010)