In summary, an in situ acidic microenvironment was constructed via the Brønsted acid oxide MoO_3-x, significantly enhancing the performance of PEM electrolysers in impure water (e.g., tap water) and effectively reducing reliance on high-cost ultrapure water. This "local microenvironment regulation" strategy can be extended to seawater electrolysis. By maintaining a low cathode pH (<2) to inhibit Mg²⁺/Ca²⁺ precipitation and combining anode anti-chlorine modification to avoid Cl^- side reactions, it is expected to realize direct and efficient hydrogen production from seawater. It is worth noting that the 10-day accelerated cycling test showed low Mo leaching rate and stable MoO_3-x structure, but further evaluation of its dissolution risk in long-term strong acidic environments under extreme water quality conditions is required. Current studies mainly focus on cations such as Na⁺, Ca²⁺, and Fe³⁺, while the synergistic effects of anions like Cl^- and SO2- 4 in actual water bodies remain unclear. Although low-concentration Cl^- has no significant impact on the IrO₂ anode, high-concentration Cl^- may trigger chlorine evolution side reactions, necessitating anode catalyst modification to improve anti-chlorine performance. Future research should expand application scenarios (e.g., adapting to industrial-scale electrolysers, enhancing compatibility with multi-ion contaminated systems) and deepen technological development (e.g., coupling dynamic pH regulation with AI control, developing low-cost catalysts, integrating with photovoltaic systems) to support the industrialization of "green hydrogen".