Metal halide materials show promise for solar-powered CO2 conversion to clean fuels

The dual challenges of fossil fuel depletion and climate change have intensified the urgent need for sustainable technologies that can simultaneously reduce atmospheric CO₂ and generate clean energy. With global CO₂ emissions reaching critical levels, developing efficient photocatalysts that harness solar energy to convert greenhouse gases into valuable fuels represents a cornerstone of "carbon neutrality" strategies. Metal halide materials have recently emerged as exceptional candidates for this purpose, offering tunable bandgaps, superior visible-light absorption, and remarkable charge transport properties. However, fundamental challenges including charge carrier recombination, material stability under harsh conditions, and the toxicity of lead-based compounds have hindered their widespread industrial application.

This comprehensive review, conducted by researchers from Wenzhou University and National University of Singapore, systematically examines the latest breakthroughs in both all-inorganic and organic-inorganic hybrid metal halide photocatalysts. The study delves into the fundamental mechanisms of photocatalytic CO₂ reduction, detailing the entire process from photon absorption and charge separation to surface catalytic reactions. The team critically evaluates four key synthesis strategies—hydrothermal methods, hot-injection techniques, ligand-assisted reprecipitation (LARP), and anti-solvent precipitation—each offering distinct advantages for controlling material composition, morphology, and scalability. The review further categorizes materials into perovskite and non-perovskite structures, analyzing how structural engineering at the molecular level influences catalytic performance.

The review highlights remarkable performance achievements across diverse material systems. All-inorganic CsPbBr₃ quantum dots demonstrated CO₂ conversion to CO and CH₄ at exceptional rates of 23.7 mmol/(g·h) with 99.3% selectivity. Size optimization revealed that 8.5 nm quantum dots achieve peak efficiency, while hybrid CsPbBr₃-Ni(tpy) composites boosted production to 431 μmol/(g·h)—26 times higher than pristine materials. Lead-free alternatives show compelling progress: Bi-based Rb₃Bi₂I₉ and Cs₃Bi₂I₉ maintained stability during week-long UV exposure, with Cs₃Sb₂Br₉ nanocrystals achieving 10-fold enhanced CO production compared to lead-based counterparts. Interface engineering breakthroughs include PML-Cu/Bi₁₂O₁₇Br₂ composites delivering 584.3 μmol/g CO yields, and oxygen vacancy-rich Bi₁₂O₁₇Br₂ nanosheets showing 15-fold improvement over bulk materials. Notably, Co-anchored BiOCl achieved 183.9 μmol/(g·h) CO generation, while MOF-encapsulated MAPbI₃@PCN-221 hybrid systems reached a total yield of 1,559 μmol/g—a 38-fold enhancement over unmodified frameworks. The review also documents the first successful conversion to C₂ products, with Rh-decorated TJU-32 producing ethanol at 50.5 μmol/(h·g) with 89.4% selectivity.

This work establishes a critical roadmap for overcoming the principal bottlenecks in photocatalytic CO₂ reduction technology. By demonstrating viable lead-free alternatives and innovative stability-enhancement strategies such as MOF encapsulation and surface engineering, the review paves the way for environmentally benign, industrially scalable catalysts. The achieved performance metrics represent orders-of-magnitude improvements in efficiency and durability, bringing solar-driven carbon valorization closer to practical deployment. Perhaps most importantly, the successful production of high-value C₂ fuels like ethanol demonstrates the potential to move beyond simple C₁ products toward economically competitive chemical synthesis. These advancements directly support global decarbonization efforts while offering a sustainable pathway for producing clean fuels and chemicals from waste greenhouse gases.