Hydrogen Production from a Relative of Fool’s Gold

Hydrogen Production
Nanoplates of a close relative of fool’s gold, a pyrite-type cobalt phosphosulfide (CoPS) catalyst (left), enhanced the light-harvesting properties of a photoelectrochemical cell that used the solar energy to produce hydrogen by splitting apart water (H2O). Films integrated into the cell (right) created an efficient solar-to-hydrogen cell using Earth-abundant cobalt rather than rare and expensive metals.

Using sunlight to produce hydrogen fuel could play a key role in enabling a low-carbon, secure energy future. Scientists discovered a pyrite-type compound, similar to fool’s gold that is competitive with platinum for splitting water to produce hydrogen. The catalyst is based on Earth-abundant materials, not rare and expensive ones. When the pyrite-type compound was incorporated into a specialized cell, it demonstrated 4.7% solar-to-hydrogen conversion efficiency, creating – to date – the most efficient solar-powered hydrogen production with Earth-abundant catalyst and semiconductor.

The Impact

Solar-driven scalable hydrogen production facilitated by abundant, affordable catalysts is a critical element of a sustainable hydrogen economy.

Summary

Scientists discovered that a close relative of a well-known iron-based mineral called fool’s gold (iron pyrite, FeS2) is an efficient catalyst for generating hydrogen by splitting water. The most active known catalysts for hydrogen generation from water splitting contain noble metals such as platinum that are expensive and relatively scarce. Earth-abundant catalysts such as the pyrite minerals (CoS2, FeS2, etc.) could help achieve affordable, efficient hydrogen production. Now researchers at the University of Wisconsin-Madison have developed a strategy to tune and further improve the catalytic activity of CoS2. Density functional theory calculations predicted that the stability and reactivity of the catalytically active sites in CoS2 could be improved by modifying the electron-donating character of the atoms bonded to cobalt, such as by substituting the sulfur (S) with the more electron-donating phosphorus (P) atom. Calculations showed hydrogen adsorption on a P site affected the hydrogen-binding energetics at the cobalt site in the ternary pyrite-type cobalt phosphosulfide (CoPS) compound, making it comparable to high-performing platinum catalyst. The researchers synthesized nanostructures (wires, platelets) and films of CoPS and tested the materials for catalytic activity in the water-splitting reaction. They found that the CoPS nanostructures were the most active Earth-abundant catalysts known to date for hydrogen generation by water splitting. Taking this discovery even further, the most efficient solar-powered hydrogen production with Earth-abundant catalyst and semiconductor was achieved with a CoPS-integrated photoelectrochemical cell. Strategies that lead to affordable, high-performance water-splitting catalysts can facilitate the implementation of the hydrogen fuel-based economy.