Multi-resolved imaging of electrocatalytic and photoelectrocatalytic oxygen evolution processes on two-dimensional transition metal dichalcogenides
image: Multi-resolved imaging reveals how different atomic defects control electrocatalytic and photoelectrocatalytic oxygen evolution on two-dimensional MoS2. Combined optical imaging and atomic-scale analysis show distinct spatial distributions of catalytic activity and charge-carrier behavior under dark and illuminated conditions.
Credit: Nano Research, Tsinghua University Press
The oxygen evolution reaction (OER) is a major bottleneck in water splitting, a key process for producing green hydrogen and other sustainable fuels. Although two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoS2 and WSe2 have emerged as promising catalysts for both electrocatalytic and photoelectrocatalytic water splitting, their performance is governed by a highly heterogeneous landscape of atomic-scale defects that has been difficult to unravel.
A research team led by Rui Hao at Southern University of Science and Technology and Song Liu at Hunan University has developed a powerful multi-resolved imaging strategy that makes these elusive processes visible in real time. By integrating in situ electrochemiluminescence (ECL), photoinduced electrochemiluminescence (PECL), and photoluminescence (PL) imaging with ex situ scanning transmission electron microscopy (STEM), the researchers were able to directly correlate catalytic activity, charge-carrier behavior, and specific defect types on individual 2D semiconductor nanosheets.
The team published their article in Nano Research on March 28, 2026.
The findings could help clarify a long-standing question in catalysis research: whether electrocatalysis and photoelectrocatalysis are governed by identical or distinct active sites. “This question has remained difficult to answer because these processes often occur under different conditions and involve different charge carriers,” said Rui Hao, corresponding author of the study. “Our imaging platform allows us to resolve how reactions and charge carriers are distributed and correlated across the material, enabling us to link specific defect types with their roles in each catalytic pathway.”
Using monolayer MoS2 as a model system, the team compared pristine samples with annealed samples containing a high density of defects. They discovered that molybdenum vacancies act as bifunctional active sites, driving oxygen evolution under both dark (electrocatalytic) and illuminated (photoelectrocatalytic) conditions. In contrast, sulfur vacancies do not serve as primary catalytic centers but significantly enhance photoelectrocatalytic efficiency by improving light absorption and promoting charge separation. “These two types of defects play fundamentally different roles,” explained Song Liu. “Molybdenum vacancies directly participate in the catalytic reaction, while sulfur vacancies mainly modulate how photogenerated charge carriers behave, which is critical for photoelectrocatalysis.”
The multi-modal imaging approach also revealed an important trade-off between activity and stability. Regions that exhibited strong photoelectrocatalytic activity were also more prone to photo-corrosion, highlighting a key challenge in designing durable photoanodes. “This spatial correlation tells us that the most active sites are often the most vulnerable,” Hao noted. “Future catalyst designs must carefully balance reactivity with long-term stability.”
Beyond MoS2, the researchers emphasize that their imaging strategy is broadly applicable to other semiconducting and catalytic materials. By providing simultaneous spatial, temporal, and chemical resolution, the method opens new possibilities for understanding complex reaction mechanisms that are otherwise hidden in ensemble measurements. Looking ahead, the team envisions using defect-engineered 2D materials for more efficient solar-driven fuel production. “Our ultimate goal is rational catalyst design,” said Hao. “By intentionally controlling the type and distribution of atomic defects, we can optimize both catalytic performance and light-harvesting efficiency, accelerating the development of next-generation energy conversion technologies.”
Other contributors include Lisi Wen, Houkai chen from the Department of Chemistry, Research Center for Chemical Biology and Omics Analysis, Shenzhen Key Laboratory of Functional Proteomics, Southern University of Science and Technology in Shenzhen, China; and Zhuojun Duan from the State Key Laboratory of Chemo and Biosensing, College of Chemistry and Chemical Engineering, Hunan University in Changsha, China; and Bo Liu from the College of Mechanical Vehicle Engineering, Hunan University in Changsha, China.
This work was financially supported by the National Natural Science Foundation of China (22374064, 22175060) and the Shenzhen Innovation of Science and Technology Commission (ZDSYS20230626090803004).
DOI Link:
https://doi.org/10.26599/NR.2026.94908340
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 8,000 articles. In 2025 InCites Journal Citation Reports, its 2025 IF is 9.4 (8.3, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.