Unraveling the intrinsic origins of defect formation in V-based alloys during hydrogen sorption cycles: nano-scale hierarchical structures induced by lattice distortion
image: A two-stage defect evolution occurred in hydrogen sorption cycles, associated with the generation of two types of nano-scale hierarchical structures. At 1st cycle, nanograins with different spatial orientations show up, which geometrically leads to the formation of dislocations between the misoriented interfaces. In subsequent cycles, alternating nano-layered structures (1 – 2 nm thickness) gradually appear within the nanograins, resulting in the formation of subgrain boundaries accompanied with the local distortion and strains.
Credit: Nano research, Tsinghua University Press
Hydrogen energy is regarded to play a critical role in the global transition to clean energy, yet its practical applications hinge on solving a critical challenge: developing durable and efficient storage materials. Vanadium (V)-based alloys, capable of reversibly storing up to 3.9 wt% hydrogen, have long been considered as promising candidates for hydrogen storage. However, the rapid degradation during hydrogen sorption cycles has hindered the applications of V-based alloys. While the defects generation and accumulation have been regarded as the core instinct factor reducing the reversible hydrogen capacity, it is still not fully understood how the defects form during the hydrogen sorption cycles in the atomic scale.
A team focusing on the hydrogen storage materials and system led by Yigang Yan at Sichuan University, Chengdu, Sichuan, China, uncovers the atomic-scale origins of the degradation and proposes actionable strategies to design stable V-based hydrogen storage alloys. Hydrogen storage systems require materials that maintain stability over thousands of cycles. Vanadium alloys, despite their high capacity at ambient conditions, suffer from irreversible damage due to defects such as dislocations and lattice strains. These defects act as hydrogen traps, reducing the ability to release hydrogen in metal hydrides. "Understanding how these defects form and accumulate at the atomic level is essential to breaking the bottleneck in V-based alloy design." explains Yigang Yan, the corresponding author and a research fellow in Institute of New Energy and Low-carbon Technology (INELT) of Sichuan University.
The team published their work in Nano research on July 25, 2025.
This work identifies atomic size difference (δ)—a measure of initial lattice distortion caused by mismatched alloying elements like titanium (Ti) and chromium (Cr)—as the primary factor governing defect formation. Researchers designed a series of V75TiCrFe2 alloys with varying δ values (3.85% to 4.32%) by adjusting Ti/Cr ratios. High-δ alloys exhibited severe degradation: after 100 cycles, the alloy with δ=4.32% lost 13.22% of its hydrogen capacity, while the low-δ alloy (δ=3.85%) retained 94.4% capacity. Plateau slope factors (Sf) and defect density, also increased significantly in high-δ alloys, further confirming their instability. Using aberration-corrected transmission electron microscopy, the team revealed a nanoscale hierarchical defect evolution process in high-δ alloys:
In the first cycle: Hydrogen absorption process triggers anisotropic lattice expansion, generating nanograins with mismatch orientations and forming the dislocations.
In the subsequent cycles: Alternating nano-layered structures (1–2 nm thickness) emerge within nanograins, creating subgrain boundaries and leading to the localized lattice distortion.
These nanostructures act as permanent hydrogen traps, irreversibly reducing storage capacity. "Low-δ alloys avoid this layered structure formation " Yan notes. "This contrast underscores the critical role of δ in defect formation and generation."
The research team proposes a clear design principle: minimization of atomic size mismatch (δ). “Replacing titanium with elements niobium (Nb) or molybdenum (Mo), which have intermediate atomic radii, could effectively reduce δ and and consequently mitigate structural degradation during prolonged cycling.” Yan explains. This work establishes a universal framework linking alloy composition, microstructure, and performance through precise control of δ. By emphasizing atomic-scale compatibility optimization, this methodology enables the rational design of vanadium-based alloys with enhanced structural stability, thereby addressing a key challenge in hydrogen storage technology. The proposed paradigm shift in materials engineering not only advances fundamental understanding of hydrogen-metal interactions but also paves the way for practical implementation in next-generation hydrogen storage systems.
Other contributors include Hanyang Kong, Qiuwei Huang, Chaoling Wu, Yao Wang and Yungui Chen from the Institute of New Energy and Low-carbon Technology (INELT) and the School of Materials Science and Engineering at Sichuan University, Chengdu, Sichuan, China. Besides, Yigang Yan, Chaoling Wu, Yungui Chen and Yao Wang are also the member of Engineering Research Center of Alternative Energy Materials and Devices, Ministry of Education, China.
This work is granted by National Key R&D Program of China (No. 2022YFB3803700) and Sichuan Science and Technology Program (PG-PGFG-JFKF23-000009-0).
About the Authors
Dr. Yigang Yan, is a research fellow in Institute of New Energy and Low-carbon Technology (INELT) of Sichuan University. He received his Ph.D. in materials science from Sichuan University in 2007. He worked as a JSPS research fellow in IMR, Tohoku University, Japan (2008-2011), a senior scientist in Empa, Switzerland (2011-2016) and a postdoc in Aarhus University, Denmark (2016-2018). At present, his research interests include hydrogen storage materials and systems, solid-state electrolytes and batteries, fuel cells and key components. He has directed 20 national and provincial projects, secured 8 national invention patents, and published 110 SCI papers (total citations: 2,658; H-index: 29; highest single-paper citations: 437). He has significantly advanced hydrogen technology through groundbreaking initiatives, including the 100-ton-scale vanadium-based hydrogen storage alloy production line and China’s inaugural solid-state hydrogen storage grid-connected power generation in the Yunnan Power Grid Photovoltaic-Hydrogen Energy Storage Demonstration Project. His work bridges academic innovation and industrial application, driving both technological progress and societal impact in clean energy.
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 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 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.