Platinum–Nickel Nanowires with Improved Hydrogen Evolution Performance in Anion Exchange Membrane-Based Electrolysis

Platinum–nickel (Pt–Ni) nanowires were developed as hydrogen evolving catalysts for anion exchange membrane electrolyzers. Following synthesis by galvanic displacement, the nanowires had Pt surface areas of 90 m2 gPt–1. The nanowire specific exchange current densities were 2–3 times greater than commercial nanoparticles and may benefit from the extended nanostructure morphology that avoids fringe facets and produces higher quantities of Pt{100}. Hydrogen annealing was used to alloy Pt and Ni zones and compress the Pt lattice. Following annealing, the nanowire activity improved to 4 times greater than the as-synthesized wires and 10 times greater than Pt nanoparticles. Density functional theory calculations were performed to investigate the influence of lattice compression and exposed facet on the water-splitting reaction; it was found that at a lattice of 3.77 Å, the (100) facet of a Pt-skin grown on Ni3Pt weakens hydrogen binding and lowers the barrier to water-splitting as compared to pure Pt(100). Moreover, the activation energy of water-splitting on the (100) facet of a Pt-skin grown on Ni3Pt is particularly advantageous at 0.66 eV as compared to the considerably higher 0.90 eV required on (111) surfaces of pure Pt or Pt-skin grown on Ni3Pt. This favorable effect may be slightly mitigated during further optimization procedures such as acid leaching near-surface Ni, necessary to incorporate the nanowires into electrolyzer membrane electrode assemblies. Exposure to acid resulted in slight dealloying and Pt lattice expansion, which reduced half-cell activity, but exposed Pt surfaces and improved single-cell performance. Membrane electrode assembly performance was kinetically 1–2 orders of magnitude greater than Ni and slightly better than Pt nanoparticles while at one tenth the Pt loading. These electrocatalysts potentially exploit the highly active {100} facets and provide an ultralow Pt group metal option that can enable anion exchange membrane electrolysis, bridging the gap to proton exchange membrane-based systems.


Figure S1 .
Figure S1.High-angle annular dark-field imaging of Pt-Ni nanowires, 7.3 wt.% Pt and annealed to 275°C.Images were used to evaluate nanowire length.

Figure S2 .Figure S3 .
Figure S2.High-angle annular bright-field (top row) and dark-field (bottom row) imaging of Pt-Ni nanowires, 7.3 wt.% Pt and annealed to 275°C.Images were used to evaluate nanowire diameter.

Figure S4 .
Figure S4.High-angle annular dark-field imaging and energy dispersive x-ray spectroscopy of Pt-Ni nanowires, 7.3 wt.% Pt and annealed to 275°C.Images were used to evaluate the Pt coating.

Figure S6 .
Figure S6.Global minimum structures of adsorbed H, OH, and H2O on Pt surfaces.

Figure S10 .
Figure S10.Climbing image nudge elastic band calculations (cNEB) for the different pathways of water-splitting on Pt (111).

Figure S11 .
Figure S11.Climbing image nudge elastic band calculations (cNEB) for the different pathways of water-splitting on Pt-Ni (111).

Figure S12 .
Figure S12.HER-HOR (a) mass (red) and site-specific (blue) exchange current densities of assynthesized Pt-Ni nanowires in RDE half-cells as a function of conditioning cycles (x-axis).Conditioning was completed in a 0.1 M perchloric acid electrolyte in the potential range 0.025-1.4V vs RHE.Activities were taken in a 0.1 M sodium hydroxide electrolyte, fit to the Butler-Volmer equation to determine exchange current densities.

Figure S13 .Figure S14 .
Figure S13.HER-HOR (a) mass (red) and site-specific (blue) exchange current densities of Pt-Ni nanowires, 7.3 wt.% Pt, hydrogen annealed to 275°C, and acid leached in RDE half-cells as a function of conditioning cycles (x-axis).Conditioning was completed in a 0.1 M perchloric acid electrolyte in the potential range 0.025-1.4V vs RHE.Activities were taken in a 0.1 M sodium hydroxide electrolyte, fit to the Butler-Volmer equation to determine exchange current densities.

Figure S15 .Figure S16 .Figure S17 .
Figure S15.Cyclic voltammograms of acid leached Pt-Ni nanowires in a 0.1 M sodium hydroxide electrolyte, prior to (Acid) and following (Acid *) conditioning in a 0.1 M perchloric acid electrolyte.Conditioning in the acidic electrolyte consisted of 100 cycles in the potential range 0.025-1.4V vs RHE at 2500 rpm and 500 mV s -1 .

Table S1 .
Adsorption Energies of Hads and OHads; reaction enthalpies for the Heyrovsky and Tafel mechanisms.

Table S2 .
Adsorption Sites of Global Minimum Structures of Hads, OHads, H2Oads