The Committee on Climate Change concluded that clean hydrogen production was essential for meeting UK's goal of net zero carbon emission by 2050. Of the 27 TWh of hydrogen produced per annum in the UK, only 1TWh of comes from direct electrolysis of water using renewable energy sources. The production of truly clean hydrogen using renewable sources requires a step change in the materials and device development. Moreover, the state-of-the-art methods utilizing renewable energy for production of hydrogen rely on expensive catalysts such as platinum, ruthenium and iridium. Thus, there is an urgent need to for reducing reliance on resource limited materials. According to a recent strategic document on clean production of hydrogen developed by the Sir Henry Royce Institute (SHRI), photochemical methods for clean production of hydrogen offer an attractive strand for high risk/high reward research activity for the UK. The SHRI suggests that for solar to hydrogen to be viable, an increase in efficiency from 1% to 10 - 15% is required through development of new catalysts and photo-electrode materials. High efficiency PEC cells for water splitting could be disruptive and the UK is in a world leading position to realize and translate this technology. To reap the benefits of PEC cells for clean hydrogen production, fundamental limitations of long-term stability of photo-electrodes with band gaps between 1 - 2 eV must be overcome. A photochemical cell typically uses semiconductor/liquid, which depending on the band-edge position can initiate HER or OER or both, whereas in a PEC, the semiconductor is usually a wide band-gap material that also serves as the photocatalyst. For photochemical cells, a mandatory requirement is for the semiconductor to be stable in aqueous media and this is a key challenge. On the other hand, PECs employing wide band-gap catalysts are stable but the efficiency is around 1%, thus making them impractical for large scale generation of hydrogen.

This proposal aims to pioneer photo-electrodes (cathodes and anodes) that overcome the current limitations using layered 2D halide perovskites as extremely efficient light absorbers and voltage sources - with the motivation to understand key processes that underpin their stability so that devices with unprecedented energy efficiency and performance can be realized. The proposal builds on our recent breakthroughs in HER and OER catalysts (Science 2016, Nature Materials 2019) as well as pioneering work in efficient and stable hybrid perovskite solar cells (Nature, 2018 & 2020). It also builds on strategic investments in the Materials for Energy Transition theme at Cambridge through the SHRI. Our ambition is to achieve band gap tunable layered 2D perovskites with ideal band offsets that are electronically coupled to inexpensive and earth abundant HER and OER catalysts through mechanical/environmental barriers that will address and overcome the long-standing challenge of realizing high efficiency PEC cells with simple device design. The proposed work will underpin and impact ongoing programmes and initiatives aligned with several EPSRC priority areas in energy materials. This includes adaptation operando characterization of catalyst materials, 2D materials and stable operation of perovskites for solar cells. This proposal aims to bring a step-change and establish an internationally leading programme in solar production of hydrogen using high- performance PEC cells based on two-dimensional catalyst materials and hybrid perovskites as photo-electrodes that will add value and connect a broad range of communities. The proposed work will open up new pathways for achieving in-depth fundamental knowledge of physics of novel devices based on 2D and hybrid perovskite materials to accelerate their development towards technological readiness and commercialization in higher value-added products.