At present, sustainable conversion efficiencies of incident solar radiation to liquid fuels are only a few percent. Harvesting ~0.25% of the ubiquitous and vast incident solar radiation on the earth (some 120,000 TW) and conversion at ~8.5-10% efficiency (i.e., ~25-30 TW) would meet the projected doubling of domestic, transport and industrial needs of the world’s population by mid-century (from ~17 TW today to ~30-35 TW). Although solar energy is diffuse and subject to diurnal and seasonal fluctuation, it does, in large part, overcome fundamental intermittency/volatility problems associated with other renewable-energy forms, e.g., wind and wave. However, although no system including a single photo-absorber has shown truly efficient, sustainable and economic water splitting to date, the gap is certainly closing with respect to non-renewables for conversion of solar energy into hydrogen or electricity from photoelectrochemical (PEC) and photovoltaic (PV) approaches, or, equally, tandem-cell approaches. In particular, PEC has seen some major developments in recent years, to the point of potentially being competitive with PV methods for real-world deployment in the coming years [1-4], with recent near-unity internal quantum efficiency [5].

  This timely workshop aims to bring together both leading experimentalists and theorists/simulators to share their perspectives, knowledge and experiences on state-of-the-art progress in both PEC and heterogeneous catalysis. The high-level workshop goals will centre around tackling the pressing problem of removing obstacles towards efficient and sustainable PEC water-splitting and CO₂ reduction - using a broad suite of state-of-the-art molecular-simulation methods to elucidate mechanistic insights for leading, careful experiments to investigate. In so doing, we advocate a pragmatic philosophy of simulation-led electronic/atomistic design as a cost-effective prototyping tool. On PEC, the workshop will elucidate the role of doping and surface defects in promoting cost-effective metal oxides’ efficiencies, such as TiO₂, Ta₂NO₅, Fe₂O₃, etc – by modulating electronic structure and excited-state properties.

  However, beyond PEC per se, this workshop will also have important goals in heterogeneous catalysis – in particular, CO₂ reduction (e.g., with in-situ or operando characterisation [6]):

1. The interface between machine learning [7], continuum-modelling approaches and experiment (for theory-predictive design of materials with optimal electric/optical properties)

2. Handling amorphous materials in simulations

3. Calculating kinetic parameters in theory and simulations

4. Simulating nano-particles and experimental use and applications of these for coating photo-absorbing surfaces

5. static electronic structure and excited-state Density Functional Theory-based calculations (e.g., non-adiabatic MD for electron-injection kinetics), emphasising dynamics and statistical distribution of charge carriers (e.g., polarons);

6. molecular dynamics of explicitly-solvated surfaces by reactive force-fields, tight-binding MD approaches and linear-scaling electronic-structure methods;

7. training of highly sensitive machine-learning potentials to allow for higher-fidelity and longer-time deterministic or free-energy-biased dynamics simulations (e.g., to gauge charge-carrier dynamics more rigorously);

8. experimental spectroscopy determinations of charge-carrier lifetimes, and on how this can drive forward progress in state-of-the-art molecular simulation;

9. development of optimal cross-laboratory validation approaches for consistent experimental measurement of solar-to-hydrogen (STH) performance metrics;

10. optimal PEC solar-cell design and real-world considerations on cell engineering and performance and longevity, including photo-corrosion and materials degradation.

  The “paradigm shift” in boosting heterogeneous catalysis’s longer carrier dynamics, as well as reducing charge recombination and canny band-gap manipulation, will serve to facilitate the development of sensible atomistic/electronic “design rules” for experiment and theory/simulation working hand in glove in a symbiotic relationship – a genuine overhaul of intellectual infrastructure and thinking. This will also help to enhance a collaborative community of problem-solving experimentalists and theorists to drive forward greater real-world impact and engineering in heterogeneous catalysis.

  We must emphasise the inherent inter-connectedness of each of the inter-disciplinary areas/goals detailed above. For instance, leveraging mechanistic/theoretical insights helps to increase the performance of photo-/electro-catalysts. These innovations can be later integrated into devices/reactors, which require specific (and standardised) testing protocols/metrics.

  Although, admittedly, we have a good number of (crucially, inter-connected and complementary) goals in the present workshop-proposal, this is quite a deliberate choice - to showcase both the ambition and skills of our inter-disciplinary team in the highly necessary and pragmatic art of achieving progress on a number of related fronts in order to have tangible impact on the heterogeneous-catalysis challenge as a whole.