image: Transmission Electron Microscope (TEM) images show CsPbBr3 nanowires with no strain (NW-NS, left), low strain (NW-LS, middle), and high strain (NW-HS, right). The curvature increases with strain due to internal lattice mismatch.
Credit: ©Science China Press
Researchers at the University of Electronic Science and Technology of China (UESTC) have made a major advance in solar-driven carbon dioxide (CO2) conversion. They developed a novel method to enhance the efficiency of metal-halide perovskite photocatalysts by precisely controlling internal lattice "tension," known as strain. This strategy led to a fivefold increase in the production rate of carbon monoxide (CO) fuel compared to conventional materials.
A key challenge in solar fuel production is the rapid recombination of light-generated electrons and holes within the catalyst before they can drive chemical reactions. To overcome this, the UESTC team engineered cesium lead bromide (CsPbBr3) perovskite nanowires with varying degrees of uniform, biaxial tensile strain (0% to 1%) by creating an internal lattice mismatch with a secondary cesium lead pentabromide (CsPb2Br5) phase during synthesis.
Performance tests in photocatalytic CO2 reduction revealed that the nnanowires with a moderate tensile strain of 0.47% (labelled NW-LS) delivered the optimal performance: a CO production rate of approximately 150.2 micromoles per gram per hour (μmol g-1 h-1). Crucially, this represents a fivefold increase over unstrained nanowires while maintaining 100% selectivity for CO production. The catalyst also demonstrated excellent stability during long-term operation.
By employing ultrafast spectroscopy (femtosecond transient absorption), in-situ infrared spectroscopy (DRIFTS), and density functional theory (DFT) calculations, the team uncovered the mechanism behind this significant improvement. They identified two key effects of the tensile strain:
1. Polaron Regulation Slows Charge Recombination: The soft perovskite lattice readily forms quasiparticles called polarons, where charges coupled with lattice distortions. The introduced tensile strain significantly enhances this lattice distortion caused by both electron and hole polarons, creating a larger energy barrier and effectively slowing down the recombination of photogenerated electrons and holes. Ultrafast measurements confirmed the longest decay component increased from 672 picoseconds in unstrained nanowires to 2.85 nanoseconds in the optimally strained sample.
2. Lowered Reaction Barrier: The strain modifies the electronic structure at the catalyst surface, shifting the energy level of the lead (Pb) atom's p-orbital upwards. This enhances the interaction with reaction intermediates, lowering the thermodynamic energy barrier for forming the critical *COOH intermediate – the rate-determining step in converting CO2 to CO. In-situ spectroscopy showed faster accumulation of *COOH on the strained catalyst surface.
"This work provides profound insights," said corresponding author Jianping Sheng. "We demonstrate that strain engineering is a powerful tool not just for tweaking electronic properties, but for fundamentally controlling polaron behavior – a key determinant of charge dynamics in soft lattice materials like perovskites. This opens exciting new avenues for designing highly efficient photocatalysts and electrocatalysts."
The performance of the strained nanowire surpasses many state-of-the-art perovskite-based photocatalysts, highlighting the immense potential of strain engineering for advancing solar fuel technologies.
About the University of Electronic Science and Technology of China (UESTC): UESTC is a leading research university in China, renowned for its strengths in electronic information technology and materials science. The School of Resources and Environment and the Institute of Fundamental and Frontier Sciences focus on cutting-edge research in energy materials, environmental catalysis, and pollution control.