Catalyst integration and light-intensity studies on surface composition effects in ZnTe photocathodes for CO 2 reduction Christina Roukounaki 1 , Sehun Seo 1 , Guosong Zeng 2,3,4 , Guiji Liu 2,3 , Olivia J. Alley 2,3 and Francesca M. Toma 1,2,3,5 * 1 Institute of Functional Materials for Sustainability, Helmholtz Zentrum Hereon, Kantstrasse 55, Teltow 14153, Brandenburg, Germany, 2 Liquid Sunlight Alliance, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States, 3 Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States, 4 Department of Mechanical and Energy Engineering, Southern University of Science and Technology, Shenzhen 518055, China, 5 Faculty of Mechanical and Civil Engineering, Helmut Schmidt University, Hamburg 22043, Germany *Corresponding Author Email: Francesca.Toma@hereon.de The photoelectrochemical (PEC) light-driven reduction of CO 2 into useful chemicals is considered a promising approach to achieving net zero carbon emission targets. ZnTe is a promising material for CO2RR, due to its light-harvesting suitable band gap and highly negative conduction-band-edge position. The influence of the photoelectrode's very top surface as well as the semiconductor/electrolyte interface have a pivotal importance for PEC CO 2 reduction but remains poorly understood. Here, we report an electrodeposition-annealing route for tailoring the surface composition of ZnTe photocathodes. The work demonstrates that a Zn-rich surface on the ZnTe photocathode, as well as the annealing temperature, is essential to impact the CO 2 reduction activity and selectivity. The Zn-rich surface acts as an electrocatalyst that enhances carbon product selectivity and suppresses the hydrogen evolution reaction, while simultaneously facilitating interfacial charge carrier transfer. 1 Building upon these findings, our work explores optimization through catalyst integration in an effort to further enhance the selectivity and activity of the ZnTe photoelectrodes. We are also investigating how light intensity can affect charge transfer dynamics, kinetics, and product selectivity. This work provides new pathways to optimize the photocathode while improving CO2RR performance by further understanding the top surface of the photocathode, the annealing route of synthesis, the catalyst integration, and light intensity. References 1. Guosong Zeng, Guiji Liu, Gabriele Panzeri, Chanyeon Kim, Chengyu Song, Olivia J. Alley, Alexis T. Bell, Adam Z. Weber, and Francesca M. Toma, “Surface Composition Impacts Selectivity of ZnTe Photocathodes in Photoelectrochemical CO2 Reduction Reaction”, ACS Energy Letters 2025 10 (1), 34-39
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