A nickel–molybdenum anode sustained a current density of 3 amperes per square centimetre in a small water-electrolysis cell across 1,200 test hours, researchers report in a study published Sept. 24 in Nature Sustainability. The anion-exchange-membrane cell had a 1-cm² active area and ran at 65°C in six 200-hour intervals, with electrolyte replenishment and system restarts.
Water electrolysers split water into hydrogen and oxygen. The oxygen-producing reaction at the anode is a performance bottleneck. The team modified a nickel-felt electrode by introducing molybdenum atoms beside nickel atoms, forming asymmetric Mo–Ni pairs with a measured spacing of 2.85 ångströms.
The authors propose that the paired sites change how oxygen forms. In the usual single-site sequence, oxygen-containing species build up on one metal site before oxygen gas leaves. The proposed oxide-path mechanism lets species on neighboring Mo–Ni sites couple directly. Isotope-labelled oxygen tests, spectroscopy and calculations support this interpretation.
The paper reports a separate 2,000-hour test at the same 3 A/cm² current density, but that was a three-electrode experiment on a 0.25-cm² electrode in 1 mol/L potassium hydroxide at 25°C, not the membrane electrolyser. The setup was restarted and its electrolyte replenished every 150 to 200 hours. For the 1-cm² membrane-cell durability test, the team lowered the temperature to 65°C after the commercial membrane let substantial water pass through it during operation beyond 100 hours at 80°C.
In a separate scale-up test, the team fitted the catalyst to a 333-cm² cell in a commercial-format alkaline electrolyser operating at 90°C with 30% potassium hydroxide. Under the cited industry protocol, it reached a rated peak current density of 1.03 A/cm² at 2 volts, 26.5% higher than the rated peak current density measured with commercial nickel felt under the same protocol. The paper’s $1.81-per-kilogram hydrogen cost is a model for an idealized 1-megawatt plant that assumes, among other inputs, wind electricity at $0.033 per kilowatt-hour; it is not a measured plant cost. These larger-cell results are separate from the 1,200-hour membrane-cell test.
Sources
- The Nature Sustainability study
- Supplementary information, including test conditions and the cost-model assumptions
- Illustrative diagram: Kavin Teenakul / Gary thelake, via Wikimedia Commons, licensed under CC BY-SA 4.0. The diagram is unmodified and does not show the study’s apparatus.
