Polyoxometalates and their derivatives: structural tuning of versatile electrocatalysts for water splitting

Electrocatalytic water splitting is a promising energy-conversion technology for green hydrogen (H2) production. However, the high cost and limited availability of noble-metal catalysts substantially impede its widespread commercialization. Polyoxometalates (POMs) and their derivatives have emerged as versatile and low-cost electrocatalytic alternatives due to their well-defined molecular structures, tunable active centers, reversible redox characteristics, and robust chemical stability. Most existing POM-related reviews merely focus broadly on generalized material applications or independently describe hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance separately, without systematically addressing structural-tuning mechanisms or the quantitative catalytic advantages of POM-based water-splitting electrocatalysts. To fill this research gap, this review systematically summarizes the structure-activity relationship of typical POM frameworks (e.g., Keggin, Wells-Dawson, Anderson) for water splitting electrocatalysis. Representative POM-based composites and POM-derived metal compounds exhibit competitive catalytic performance: optimized POM-based electrodes can achieve overpotentials of 80-150 mV for the HER and 150-300 mV for the OER at a current density of 10 mA cm-2. We comprehensively analyze the structural advantages of POMs in modulating electron transfer and optimizing reaction intermediate adsorption, and further discuss core limitations including insufficient intrinsic conductivity, particle aggregation, and structural dissolution during electrocatalysis. Finally, targeted structural tuning and composite engineering strategies are proposed to advance the development of high-performance, versatile POM-based electrocatalysts for efficient water splitting.