Exposure of single-walled carbon nanotubes (CNTs), as well as other lower cost layered graphitic carbons (LGCs), to acidic intercalants, in combination with low voltage electrochemical cycling, induces in these materials hydrogen evolution activity that initiates at near zero overpotential and is on par with that of platinum catalysts.¹ These results encouraged the further development and testing of the CNT catalyst in a PEM water splitting electrolyzer prototype. Once activated, the CNT cathode demonstrated 1 A/cm² of HER current at 1.64 V, comparable to a similarly tested commercial Pt-loaded cathode. While carbon nanotubes are not intrinsically scarce, the single wall nanotubes used in these electrode tests remain relatively expensive. Commercial significance would benefit from a demonstration of comparable performance from activated lower cost layered graphitic carbons in a PEM electrolyzer prototype.

The following LGC materials, having a combination of high electrical conductivity, large pore volumes, and high specific surface areas, were tested in terms of their ability to achieve low HER overpotential during the activation process: microcrystalline graphitic particles, Vulcan XC-72 carbon, highly graphitized stacked-cup tubular carbon nanofibers (CNFs), and carbon needle felt. CNF electrodes demonstrated slightly higher mass basis activity than that of the other tested LGCs in acid electrolyte in a standard three-terminal electrochemical cell.

Here we report excellent performance from activated CNF cathodes, prepared by a scalable spray-coating method, in our PEM electrolyzer prototype (IrRuO_x as anode catalyst). As anticipated, a control MEA, based on the non-activated CNF cathode and tested in PEM electrolyzer under identical conditions, showed poor performance, indicating a low electrocatalytic HER activity of the electrode.

The activated CNF cathode-based PEM electrolyzer achieved 1 A/cm² at 1.78 V, while a control commercial MEA with Pt-loaded cathode/IrRuO_x anode (a high Pt catalyst loading of 3 mg/cm² cathode, Fuel Cells Etc) tested in the same PEM electrolyzer cell demonstrated 1 A/cm² at 1.7 V.

Acknowledgements.

This work is supported by Amazon through ECS Amazon Catalyst Program.

References:

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