Inspired　by　the　metal-oxo　cluster　structural　feature　and　charge　separation　behaviour　of　the　oxygen　evolving　center　(OEC)　in　photosystem　II　(PS-II)　under　photoirradiation,　a　new　crystalline　photochromic　polyoxomolybdate,　MV2[beta-Mo8O26]　(1,　MV=methyl　viologen　cation),　is　designed　as　a　biomimetic　oxygen　evolution　reaction　(OER)　catalyst　in　neutral　electrolytes.　After　photoinduced　electron　transfer　(PIET)　with　colour　change　from　colourless　to　grey,　it　remains　in　an　ultra-stable　charge-separated　state　over　a　year　under　ambient　conditions.　The　observed　overpotential　at　10　mA　&　sdot;　cm-2　and　Tafel　slope　decrease　by　49　mV　and　62.8　mV　&　sdot;　dec-1　after　coloration,　respectively.　The　outstanding　OER　performance　of　the　coloured　state　in　neutral　electrolytes　even　outperforms　the　commercial　RuO2　benchmark.　Experimental　and　theoretical　studies　show　that　oxygen　holes　within　polyanions　after　irradiation　serve　as　sites　for　enhancing　direct　O-O　coupling,　thus　effectively　promoting　OER.　This　is　the　first　successful　application　of　electron-transfer　photochromism　to　realize　OER　activity　gain.　Electron-transfer　photochromism　is　used　to　enhance　the　oxygen　evolution　reaction　(OER)　activity,　providing　an　innovative　design　concept　for　the　development　of　non-precious　metal　OER　catalysts　in　artificial　photosynthesis　devices.+image