(Invited) Controlled Synthesis of Cocatalyst-Semiconductor Hybrid Nanomaterials for Photocatalytic Water Splitting
Authors: Saruyama Masaki 
Published: August 2024

With the escalating global demand for energy, mitigating anthropogenic climate change necessitates the pursuit of carbon-neutral energy sources to diminish reliance on fossil fuels. Utilizing particulate photocatalysts for solar-light-driven water splitting presents a promising and sustainable paradigm for the large-scale production of storable and clean H2 fuel. To improve the solar energy conversion efficiency, coupling the photocatalysts with cocatalysts is a broadly adopted approach not only to facilitate charge separation and transport but also to serve as reaction sites and accelerate water-splitting reactions. Recent breakthroughs in colloidal synthesis enable the fabrication of advanced nanoparticles with precise control over size and composition. Colloidal NPs represent ideal cocatalyst candidates due to their capacity to provide numerous active sites and facilitate uninterrupted light absorption by the semiconductor. Here, we introduce our approach to synthesize cocatalyst-semiconductor hybrids as efficient photocatalysts, including the alloying of platinum group metal nanoparticle cocatalysts and the control of single-atom cocatalyst locations on semiconductor nanoparticles.

Platinum group metals exhibit high efficiency as cocatalysts in the hydrogen evolution reaction, attributed to their favorable catalytic and electronic properties. Bimetallic alloy systems, in general, can considerably modulate their electronic structures, resulting in exceptional physicochemical properties surpassing those of their monometallic counterparts. Herein, we synthesized PtRu solid-solution alloy nanoparticles as high-performance H2 evolution reaction cocatalysts. The rational integration of PtRu nanoparticles with Al-doped SrTiO3 photocatalyst through liquid-phase adsorption and successive two-step annealing ensure the uniform deposition of PtRu alloy nanoparticles with a solid-solution structure. The bimetallic synergy between Pt and Ru induces higher electrocatalytic activity for the hydrogen evolution reaction and a superior electron-capturing property than its Pt counterpart. Modification of Al-doped SrTiO3 with PtRu alloy nanoparticles, CrOx, and CoOOH results in efficient photocatalytic overall water-splitting activity with an apparent quantum yield of 65% at 365 nm. This work introduces a framework to elucidate catalytic trends, offering rational design guidance for the development of bimetallic solid-solution nanoparticles as highly active cocatalysts for overall water splitting.

Single-atom cocatalysts dispersed on semiconductor materials exhibit outstanding heterogeneous catalytic properties through the interactions between the single atoms and the photocatalyst. The nature of these interactions depends on whether the single atoms are located on the surface or within the interior of the photocatalyst. In this work, the location-selective placement of single atoms is achieved by carefully adjusting experimental procedure. Using CdSe nanoplatelets as a support, applying different Pt precursor complexes, solvent, and workup process resulted in location selective deposition of Pt atoms outside/inside CdSe nanoplatelet support. In photocatalytic hydrogen evolution reaction, the surface-adsorbed single Pt atoms exhibit higher stability than the substituted ones. This study provides a viable strategy for the structurally precise synthesis and design of single-atom catalysts.