Annual Review 2024-2025

A N N U A L R E V I E W 2 0 2 4 / 2 5 32 S T R U C T U R E S A N D S U R FA C E S G R O U P Advances in seawater electrolyte-assisted photocatalysis The photocatalytic process of water-splitting uses sunlight to break down water molecules into hydrogen and oxygen gases with a light-absorbing catalyst. Using seawater has so far been limited by poor energy conversion efficiencies, instability, and the negative effects of electrolytes in seawater at room temperature. In addition, high electricity consumption and desalination capital costs have impaired technological advancements. The focus of research led by a team from the University of Oxford was to understand how electrolyte-assisted charge polarisation could influence the photocatalytic performance of nitrogen- doped titanium dioxide (N-TiO 2 ) in seawater (N-TiO 2 is a semiconductor and a versatile photocatalyst). This type of polarisation could increase the lifetime of charged species on the surface of the photocatalyst for splitting water into hydrogen and oxygen. The results demonstrate that N-TiO 2 , under electrolyte-assisted polarisation, can achieve a higher solar-to-hydrogen conversion efficiency of 15.9% at 270°C, surpassing previous conversion efficiencies of <5% using other photocatalysts. Ionic species in seawater were also found to prolong the charge-carrier lifetime, significantly enhancing photocatalytic activity. Diamond’s B07-C beamline was used to study charge separation and distribution on the photocatalyst’s surface at an atomic level. B07-C is ideal because it specialises in providing gas delivery systems that deliver the well-defined compositions of gases a catalyst might be exposed to, using a computer-controlled environment that can be managed remotely. The surface-sensitive Near- Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) technique and trimethylphosphine (TMP) as the surface probe were deployed to investigate the surface charge transfer/accumulation on different crystal facets of the photocatalyst at different temperatures, ranging from 150 to 270°C. Concept plans have been drawn up for a commercial scale solar farm to produce green hydrogen from thermal assisted photocatalytic splitting of seawater. Ultimately, the goal is to promote energy security through decentralised, local production facilities, paving the way for exploration into scaling up the technology for industrial applications. DOI: 10.1038/s41929-023-01069-1 A D B E C F Computational study of the electrolyte-assisted photocatalytic overall water splitting (POWS) system.