Applied Surface Science | Asymmetric Cu–O–Ti Dual Sites Drive Charge Localization for Enhanced Photocatalytic Hydrogen Evolution

Article Highlights

Solar-driven photocatalytic water splitting offers a sustainable route to hydrogen and can help address global energy and environmental challenges. TiO₂ is widely regarded as a benchmark photocatalyst because of its abundance, chemical stability and appreciable ultraviolet-light activity, yet rapid photocarrier recombination and a shortage of active sites limit practical performance. This study addresses both issues by engineering asymmetric Cu–O–Ti dual sites. Cu single atoms are anchored on TiO₂ by hydrothermal synthesis and calcination. The electronic asymmetry of the resulting Cu–O–Ti motif creates a built-in electric field directed from Cu toward Ti. Cu₁–Ti/TiO₂ achieves a hydrogen-evolution rate of 1.91 mmol g⁻¹ h⁻¹—63.67 times that of pristine TiO₂ and among the leading values for TiO₂-based photocatalysts. The internal field promotes photocarrier separation and directs electrons into Cu 3d orbitals. Ti sites preferentially adsorb and dissociate H₂O, while Cu sites mediate H adsorption and H₂ formation, creating an efficient division of catalytic functions.

Introduction

In March 2026, Applied Surface Science published the latest work on photocatalytic hydrogen evolution from the teams of Senior Engineer Hanjun Zou at Chongqing University and Dr. Yang Wang at Chongqing University of Posts and Telecommunications. The study reports asymmetric Cu–O–Ti dual active sites for efficient photocatalytic hydrogen production. Hanjun Zou is the first author; Yang Wang, Chunyu Li and Chaogang Ban are co-corresponding authors.

Background

Solar-driven water splitting provides a sustainable route for alleviating energy and environmental problems. Among semiconductor photocatalysts, TiO₂ is especially attractive because of its abundance and excellent stability. Pristine TiO₂ nevertheless suffers from severe photogenerated-carrier recombination and an insufficient density of active sites. New architectures must therefore combine efficient carrier separation with abundant, well-defined catalytic centers.

Asymmetric dual sites offer a promising solution. Coupling the intrinsic Ti sites of TiO₂ with an externally introduced metal site can induce charge redistribution and generate a built-in electric field that accelerates carrier separation. Here, earth-abundant Cu is coupled with TiO₂ to create Cu–O–Ti asymmetric dual sites. Cu captures electrons, suppresses carrier recombination and directly participates in the catalytic cycle. Strong electronic coupling between Cu and adjacent Ti atoms further enhances interfacial charge transfer and improves the reaction kinetics.

Equipment Used in This Study

The study used the PerfectLight μGAS1000 Trace Gas Reaction Evaluation System. Developed from PerfectLight’s extensive experience with gas-tight glass reaction systems, the instrument is designed for photocatalysis experiments that generate trace amounts of gas, including photocatalytic water splitting and photocatalytic CO₂ reduction.

Figures and Analysis

Key Point 1 · Atomically Dispersed Cu and Its Local Coordination Environment

Cu₁–Ti/TiO₂ was successfully prepared by hydrothermal synthesis and calcination. Aberration-corrected HAADF-STEM images show isolated Cu atoms uniformly dispersed on the TiO₂ support. XAFS places the Cu absorption edge between those of Cu₂O and CuO, indicating a partially positive Cu state. The FT-EXAFS spectrum shows only a Cu–O coordination peak at 1.45 Å and no Cu–Cu peak, confirming atomic dispersion and the successful formation of asymmetric Cu–O–Ti dual sites.

Key Point 2 · Directional Charge Migration Driven by the Built-In Electric Field

In situ XPS and theoretical calculations reveal the charge dynamics at the asymmetric sites. In the dark, electrons transfer from Cu toward TiO₂, generating a built-in electric field directed from Cu to Ti. Under illumination, the Ti 2p signal shifts to higher binding energy while Cu 2p shifts to lower binding energy, demonstrating that photogenerated electrons move from TiO₂ along the internal field and accumulate at the Cu single-atom centers. Femtosecond transient-absorption spectroscopy further confirms that the Cu sites act as efficient electron traps and accelerate charge separation.

Key Point 3 · Cooperative Catalytic Functions Lower the Hydrogen-Production Barrier

DFT calculations show that H₂O preferentially adsorbs on Ti sites with an adsorption energy of −0.97 eV and then dissociates there. Cu sites are more favorable for H adsorption and H₂ formation: the H₂-formation barrier is only 1.35 eV at Cu, far below the 2.94 eV barrier at Ti. H₂-TPD shows a shift of the desorption peak toward lower temperature for Cu₁–Ti/TiO₂, confirming that Cu single atoms facilitate H₂ desorption. This cooperative division—Ti for H₂O adsorption and dissociation, Cu for H adsorption, H₂ formation and desorption—substantially increases photocatalytic hydrogen-evolution activity.

Summary

By anchoring Cu single atoms on TiO₂ nanoparticles, this study constructs Cu₁–Ti/TiO₂ with asymmetric dual sites. The catalyst reaches a hydrogen-evolution rate of 1.91 mmol g⁻¹ h⁻¹ and maintains good stability. The asymmetric Cu–O–Ti structure generates a built-in electric field directed toward Ti, driving electrons into Cu 3d orbitals and suppressing carrier recombination. Ti sites adsorb and dissociate H₂O, whereas Cu sites substantially lower the kinetic barrier for H₂ formation and promote desorption. This cooperative mechanism optimizes the reaction pathway and offers an important design principle for efficient, engineered solar-to-hydrogen photocatalysts.

Author Profiles

Hanjun Zou

Senior Engineer, Analytical and Testing Center, Chongqing University

Hanjun Zou has extensive experience in the management and maintenance of large instruments, including X-ray diffractometers and chemisorption analyzers, and focuses on the preparation, characterization and performance of photoelectrocatalytic materials. Over the past five years, Zou has published more than 30 SCI-indexed and core-journal papers, including seven as first or corresponding author, and holds one granted invention patent and one utility-model patent. Honors include first prize in the 2021 Science and Technology Award of the China Association for Instrumental Analysis and third prize in the 2023 Outstanding Young Talent Award for University Analytical Testing.

Yang Wang

Lecturer, Chongqing University of Posts and Telecommunications

Dr. Wang studies structure–property relationships in integrated nanomaterials, including material structure, reaction kinetics and performance-enhancement mechanisms. His expertise also covers experimental characterization, design and theoretical analysis for water/gas adsorption, coating, modification and weather-resistance improvement in functional materials. Over the past five years, he has published 16 SCI papers as first, co-first or corresponding author in journals including Energy & Environmental Science, Advanced Functional Materials and Nano Energy. Three are ESI Highly Cited Papers and two are Hot Papers; his work has received 3,177 citations and his H-index is 28. He has filed four Chinese invention patents and received awards from the Sichuan–Chongqing Science and Technology Academic Conference and his university.

Email: yangwang@cqupt.edu.cn

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