Researchers from the Australian National University and the University of New South Wales (UNSW) recently used perovskite solar cells for the development of a novel technology for direct solar hydrogen generation (DSTH), claimed to achieve an impressive solar-to-hydrogen efficiency of around 20%.
In DSTH systems, the electricity generated by a PV unit is used to directly drive water-splitting redox reactions without the need for an electrolyzer or complex power infrastructure. Commercial viability, however, remains unattainable despite efficiencies close to 19%, due to the use of expensive semiconductors and noble-metal catalysts.
The new systems, however, reportedly uses inexpensive semiconductors and low-cost, Ni-based catalysts, which could mean it has a real potential for scaling up.
The integrated water-splitting cell developed by the Australian group is based on a 'flower-stem' morphology and is planned to rely on a hydrogen evolution reaction (HER) electrode made of NiMo alloy, which is a non-noble-metal-based efficient catalyst for HER due to its appropriate hydrogen binding energy and excellent alkali corrosion. This electrode is then coupled with an oxygen evolution reaction (OER) electrode made of low-cost nickel-iron alloy (NiFE) that, in turn, offers an excellent OER catalytic activity.
DSHT systems are usually built with two or more single PV cells, due to the relatively high voltage requirements of the water-splitting reaction. The demonstrated system, by contrast, is powered by a single, 24.3%-efficient tandem perovskite-silicon solar cell based on a perovskite cell with a power conversion efficiency of 15.3%, an 'unprecedented' open-circuit voltage of 1.271 V, a short circuit current density of 17.8 mA/cm-2, and a fill factor of 68%.
The researchers said that the high voltage obtained in their work proved to be decisive in the optimal matching of the power generated by the tandem cell and the energy needed by the catalyst electrodes to split water, thereby resulting in high solar-to-hydrogen efficiency.
The surface of the perovskite layer was passivated with an organic cation known as n-dodecylammonium bromide (C12H28BrN), which consists of a long alkyl chain. The tandem cell was linked to the cell catalyst electrodes with wired connections.
The scientists said their analysis demonstrated that the proposed system may achieve solar-to-hydrogen efficiency of 20% at a levelized cost of hydrogen (LCOH) estimated at $4.10/kg. 'Improving solely the perovskite cell could enhance the STH efficiency close to 25%,' they said. 'Combined with future reductions in the PV panel and membrane costs, an LCOH of $2.30/kg-1 could be achieved, presenting a remarkable opportunity to realize cheap renewable hydrogen.'
The scientists estimate that in order to make the DSTH technology practically viable, the next vital steps are reactor optimization to produce H2 gas at scale in a cost-effective manner, and achieving the technology readiness needed for market adoption.