Many MindedWhy cobalt phosphide survives the conditions that should destroy it
A study in the Journal of the American Chemical Society, with Zhongyuan Guo as first-listed author and a news release issued through Tohoku University, explains a puzzle about cobalt phosphide (CoP), a candidate to replace platinum in splitting water into hydrogen. Computer models had predicted CoP should be unstable under hydrogen-production conditions. Experiments show it stays active and durable in acidic, neutral and alkaline solutions.
The study finds that CoP's surface changes with the applied voltage. At lower voltages, hydroxyl groups (P-OH) form on phosphorus sites and help neighboring cobalt atoms activate water and bind hydrogen. At higher voltages, the surface becomes covered with hydrogen-containing species (Co-H and P-H), which keeps binding and releasing of hydrogen in balance across pH values. These adsorbed species form a protective layer that limits oxidation and stops cobalt and phosphorus from dissolving into the solution.
The work combined AI-assisted analysis of earlier literature (2,282 observations from about 886 CoP-based catalysts in about 700 publications), computer simulations and lab experiments. Predictions were tested on specially prepared CoP nanosheets. Spectroscopy detected the predicted surface species, and deuterium tests indicated hydrogen bonding to phosphorus. The catalyst performed strongly at all three pH levels with relatively little extra voltage, and held steady for 24 hours at current densities above 1 A per square centimeter.
Why it matters: platinum is a major cost and supply constraint for electrolysis. Knowing why a cheaper metal compound lasts gives designers a rule to build around, which could help bring down green hydrogen costs.
The caveats are real. These were lab-scale tests on prepared nanosheets, not industrial electrolyzers, and stability was shown for only 24 hours. Cost benefits remain potential, not demonstrated.
Source: Phys.org