EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The current global energy crisis, caused by the depletion of fossil fuels and pollution that goes with it, has forced mankind to seek for alternative energy sources. Photocatalysis presents a viable solution for clean and renewable energy production: it allows the transformation of solar to chemical energy with the aid of a photocatalyst. Through it, the photon’s energy can be stored in the chemical bonds of “solar fuels” – commodity chemicals generated exclusively from abundant feedstocks (e.g. water or carbon dioxide), sunlight and the catalyst itself.

However, the catalytic reactions (e.g. water splitting or CO2 reduction) to produce these fuels involve kinetically complex redox processes, which limit the efficiency and applicability of contemporary photocatalysts. Besides, the most investigated photocatalysts to date rely on scarce noble metals, while more abundant transition metals remain underexplored due to their inferior performances.

In an effort to address these challenges, heterogenous single-metal-site catalysts (HSMSCs) have emerged as promising materials due to their ability to bridge the advantages of homo- and heterogeneous catalysis, generating more unique, selective and effective (co-)catalysts. In this work, we take inspiration from the concept of HSMSCs and follow the idea of site-isolation aiming towards single-site species. We synthesize a set of photocatalysts using bare and phosphate-modified TiO2 as model supports for earth-abundant metals (Cu, Ni) with various loadings (0.008-5 wt.%) as co-catalyst. These are characterized by TXRF, UV-vis and FTIR spectroscopy for elemental analysis, metal states and binding modes clarification, and also SEM, HRTEM and XRD for elucidation of the photocatalysts’ surface morphology. We evaluate photocatalytic hydrogen evolution reaction (HER) performances and show that lower co-catalyst loadings result in much higher turnover frequencies (TOFs), indicating an improved atom-utilization efficiency, reaching performances comparable the noble Au co-catalyst reference and confirming a strong structural reconstruction upon site-isolation towards smaller, perhaps even single-site-like species.