Title : Reversible redox dynamics of cocatalysts underpinning photocatalysis for solar hydrogen production
Abstract:
Efficient solar-driven hydrogen production over particulate photocatalysts provides a promising pathway towards sustainable energy and chemical conversion, yet its practical implementation remains fundamentally limited by the dynamic and often poorly controlled reconstruction of cocatalysts under operating conditions. While cocatalysts are widely regarded as static promoters of charge separation and surface reactions, their in-situ redox evolution, surface restructuring, and metal-hydrogen interactions critically dictate hydrogen evolution kinetics, selectivity, and stability. A unified understanding of how to identify, monitor, and regulate these dynamic processes has remained elusive.
In this talk, I will present a comprehensive framework that establishes cocatalyst dynamic reconstruction as a central governing principle in photocatalytic hydrogen evolution. By integrating representative systems across noble-metal cocatalysts, metal-oxide interfaces, and redox-active molecular cocatalysts, we demonstrate that rational control over cocatalyst dynamics enables suppression of parasitic reverse reactions and acceleration of hydrogen evolution.
First, I will show how selective surface reconstruction of noble-metal cocatalysts can fundamentally alter reaction pathways. Using Rh-decorated GaN-ZnO as a benchmark overall water splitting photocatalyst, atomic layer deposition of inert Al2O3 selectively passivates low-coordinated Rh sites, suppressing undesirable redox cycling and backward reactions between H2 and O2. This targeted regulation of cocatalyst dynamics leads to an order-of-magnitude increase in photocatalytic activity, enhancing the apparent quantum efficiency at 420 nm from 0.3% to 7.1%.[1]
Next, I will discuss how dynamic redox evolution of metal cocatalysts governs hydrogen evolution efficiency. Taking Pt/SrTiO3 as a model system, we reveal that the in-situ transformation of PtOx into metallic Pt is essential for efficient charge transfer and hydrogen evolution. By introducing an amorphous FeOx modifier, this dynamic reconstruction is thermodynamically accelerated and stabilized, while the metal-hydrogen interaction is weakened to facilitate rapid H2 desorption. This strategy proves to be universal across a wide range of noble and non-noble metal cocatalysts, highlighting the generality of regulating cocatalyst redox dynamics.[2]
Finally, extending the concept beyond solid-state cocatalysts, I will introduce a reversible redox-mediated cocatalysis paradigm using polyoxometalates during biomass photoreforming for hydrogen production. Through quasi-in-situ and time-resolved spectroscopic techniques, phosphotungstic acid is identified as a dynamic molecular cocatalyst that operates via a reversible PTA1e/PTA2e redox cycle. This cycle simultaneously mediates interfacial electron transfer and hydrogen release, directly correlating cocatalyst redox speciation with hydrogen evolution rates.
