Low loading of lrO2/TiO2 enabled by Pd promoter in acidic water electrolysis
image: Highly dispersed Pd-doped IrO2 nanoparticles over TiO2 support make the catalyst achieve a greatly enhanced mass activity. Pd doping results in the higher Ir(III) species amount as well as the lower Ir-O bond interaction, which improves the OER performance.
Credit: Nano Research, Tsinghua University Press
Proton exchange membrane water electrolyzers (PEMWEs) are regarded as a potential technology to generate green hydrogen as a renewable energy. Among the benchmarked electrocatalysts used in PEMWEs, IrO2 exhibits a high stability in a harsh acidic environment but a relatively low activity. It generally requires an Ir loading as high as 2-4 mgIr cm-2 to reach reasonable performance, which however, is uneconomical for such a noble metal for practical application of PEMWEs. As a result, it is urged to reduce iridium loading in PEMWEs while maintain high catalytic performance.
A team of material scientists led by Prof. Rui Lin from Tongji University in Shanghai, China recently carried out a Pd-doped IrO2/TiO2 electrocatalyst for acidic oxygen evolution reaction. The mass activity is significantly enhanced, e.g., 750.4 A gIr-1 @ 1.53 V, and the degradation rate is reduced to 0.2 mV h-1. It also exhibits a great potential for PEMWE application, as evidenced by the high activity of 1.9 V @ 3.8 A cm-2 with a low Ir loading of 0.35 mgIr cm-2, which surpasses the DOE 2025 target (3 A cm-2 @ 1.9 V).
The team published their job in Nano Research on December 3, 2025.
Tuning the OER pathways of Ir-based catalysts can effectively impact the activity. Lattice oxygen mechanism (LOM) bypasses the formation of kinetically unfavorable *OOH, one of intermediates of adsorbate evolution mechanism (AEM), to increase the reaction kinetics. However, LOM should be avoided in order to achieve stable OER performance. “The lattice oxygen participation leads to structure collapse and metal dissolution of catalysts, especially for those with low Ir loading, which makes AEM still a preferrable reaction pathway during OER process,” said Rui Lin, corresponding author of the research article, professor in the School of Automotives Studies at Tongji University.
One of the effective methods to decrease the high energy barrier of AEM, is to incorporate heteroatoms into IrO2 lattice. It can afford abundant Ir-O-M motifs to tailor the electronic structure of Ir sites. palladium (Pd) could be a promising candidate in terms of Ir substitution because of its low lattice mismatch. And the relatively low cost (one fourth of Ir) makes Pd considerable for further optimization in acidic conditions.
Pd dopants can induce a low Ir coordination environment of the electrocatalyst, thereby promoting the formation of surface Ir(III) species as active sites. The XPS-deconvoluted Ir(III) percentage exhibits an evolution trend comparable to Tafel slope with an increase of the Pd doping level, indicating the contribution of Pd-modulated active Ir(III) species to the enhanced OER performance. “We confirmed that higher surface Ir(III) species could optimize the oxygen-containing intermediates adsorption behavior, and thus a faster OER kinetics,” said Rui Lin. Besides, the Pd dopants can weaken the Ir-O bonds covalency and suppress the participation of lattice oxygen, further stabilize the structure during OER process. “Only the classical *OOH related peaks were detected during in-situ FTIR testing. Besides, a relative lower energy barrier was obtained under AEM pathway from the density functional theory (DFT) calculations,” also said Rui Lin.
When the electrocatalyst was integrated into PEMWE anode, “it exhibited a lower ohmic overpotential compared to commercial IrO2, and it also had much smaller kinetic, as well as mass transfer overpotential,” said Rui Lin, “it surpasses many previously reported Ir based catalysts employed in PEMWEs, reflecting a great potential in large-scale application.” This work offers an easy Pd doping method to modify the Ir local environment of supported IrO2 catalyst, which can be further applied in low Ir-based PEMWEs system.
Other contributors include Junxi Zhang, Xin Cai, Xin Li, Sanhuang Ke, Cunman Zhang from Tongji University; Chunjian Zhang from Yangtze River Delta Intelligent New Energy Vehicle Innovation Center; and Yuen Wu from University of Science and Technology of China.
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.