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Proton exchange membrane (PEM) water electrolysis technology has become a key approach for hydrogen production due to its high current density, high efficiency, and compact design. However, the scarcity of iridium-based anode catalysts and their high cost (around $150 per gram) pose significant barriers to its large-scale application. Recently, an innovative study proposed an iridium-free electrocatalyst (TaOₓ-MoRuO₂) consisting of tantalum oxide (TaOₓ) coated on molybdenum-doped ruthenium oxide (MoRuO₂). Thanks to the unique properties of tantalum, this catalyst achieved a double improvement in the performance for acidic oxygen evolution reaction (OER), offering a low-cost solution for commercial PEM electrolyzers. 1 Core Innovation: Dual \"protection + optimization\" benefits of tantalum oxide. By creating a TaOₓ protective layer on the surface of MoRuO₂, the research team leveraged the key advantages of tantalum to address the major shortcomings of traditional ruthenium-based catalysts: 1. Superior corrosion resistance: Tantalum exhibits excellent chemical stability in highly oxidative and acidic environments; the TaOₓ coating acts as a \"shield,\" effectively preventing the dissolution and loss of ruthenium (Ru) and molybdenum (Mo). After 150 hours of testing, the dissolution concentrations of Ru and Mo were only 1/2.7 and 1/2.5 respectively of those in the uncoated samples. 2. Precise regulation of electronic structure: TaOₓ facilitates interfacial electron rearrangement between Ru and Mo through bridge oxygen atoms, thereby increasing their electronic density and preventing excessive oxidation of Ru (such as the formation of soluble RuO₄). It also increases the concentration of oxygen vacancies (with a Oᵥ/O_L ratio of 1.32, higher than 0.81 in MoRuO₂ and 0.68 in pure RuO₂), thus significantly enhancing catalytic activity. 3. Excellent structural compatibility: TaOₓ exists on the surface of MoRuO₂ in the form of an amorphous coating, without disrupting the rutile crystal structure of the substrate, thus preserving the integrity of the catalyst’s original active sites. 2 Performance tests: Superior performance compared to traditional catalysts. 1. Catalyst activity reaches new heights: In acidic electrolytes, TaOₓ-MoRuO₂ exhibits an extremely low reaction energy barrier; only a potential of 180 mV is required to achieve a current density of 10 mA·cm⁻². This value is much lower than that of molybdenum-doped ruthenium oxide (202 mV), pure ruthenium oxide (239 mV), and commercial ruthenium oxide (286 mV). The Tafel slope is as low as 57.2 mV·dec⁻¹, indicating a significant improvement in reaction kinetics. 2. Stability exceeds industrial requirements • In a three-electrode system, continuous operation at a current density of 50 mA·cm⁻² for 150 hours resulted in a degradation rate of only 0.034 mV·h⁻¹, which is 1–2 orders of magnitude lower than that of similar ruthenium-based catalysts ； • In the tests of PEM electrolyzers, they were able to operate stably at a high current density of 500 mA·cm⁻² for 100 hours, with the cell voltage remaining around 1.64 V without any significant degradation; in contrast, both MoRuO₂ and commercial RuO₂ catalysts showed a notable decline in performance ； • After long-term operation, the catalyst retained its intact crystal structure and uniform element distribution, with the Ru³⁺/Ru⁴⁺ ratio decreasing by only 9.3%, which is significantly better than the 21.7% observed for MoRuO₂. Figure 1: Synthesis route, TEM characterization, and XRD patterns of TaOₓ-MoRuO₂. The left figure shows the synthesis scheme, while the right figure indicates that the coating does not change the crystal structure of the substrate. Figure 2: XPS and EXAFS test results, confirming the regulatory effect of TaOₓ on the valence state of Ru and the interfacial interactions. Figure 3: Polarization curves, Tafel plots, and long-term stability tests. The upper graph shows a comparison of the activity of different catalysts, while the lower graph presents the results of the 150-hour durability test. Figure 4: PEM electrolyzer setup, photos of the MEA, and performance tests. The left figure shows a schematic diagram of the single cell structure, while the right figure indicates that TaOₓ-MoRuO₂ exhibits a voltage of only 1.81 V at a current density of 1 A·cm⁻². Figure 5: XRD, TEM, and XPS patterns of the catalyst after 150 hours of OER testing, confirming the stability of its structure and chemical state. 3 Technical significance: A key step toward the large-scale use of hydrogen energy. Through the precise application of tantalum oxides, this research has led to the development of iridium-free catalysts that exhibit high activity, long lifespan, and low cost, thereby resolving the trade-off among cost, performance, and stability in PEM water electrolysis technology. Compared to traditional iridium-based catalysts, TaOₓ-MoRuO₂ features a richer ruthenium content (ruthenium costs around $19 per gram, which is only 1/8 of the price of iridium), along with the effective protective effects of tantalum; this makes it a viable option for the large-scale commercial use of electrolyzers, thereby helping hydrogen energy become a key component of clean energy in the future.