Direct solar hydrogen generation at 20% efficiency using low-cost materials

While direct solar-driven water splitting has been investigated as an important technology for low-cost hydrogen production, the systems demonstrated so far either required expensive materials or presented low solar-to-hydrogen (STH) conversion efficiencies, both of which increase the levelized cost of hydrogen (LCOH). Here, a low-cost material system is demonstrated, consisting of perovskite/Si tandem semiconductors and Ni-based earth-abundant catalysts for direct solar hydrogen generation. NiMo-based hydrogen evolution reaction catalyst is reported, which has innovative “flower-stem” morphology with enhanced reaction sites and presents very low reaction overpotential of 6 mV at 10 mA cm⁻². A perovskite solar cell with an unprecedented high open circuit voltage (V_oc) of 1.271 V is developed, which is enabled by an optimized perovskite composition and an improved surface passivation. When the NiMo hydrogen evolution catalyst is wire-connected with an optimally designed NiFe-based oxygen evolution catalyst and a high-performance perovskite-Si tandem cell, the resulting integrated water splitting cell achieves a record 20% STH efficiency. Detailed analysis of the integrated system reveals that STH efficiencies of 25% can be achieved with realistic improvements in the perovskite cell and an LCOH below ≈$3 kg⁻¹ is feasible.