Keggin-type polyoxometalate anions [XM 12 O 40 ] nÀ are versatile,a st heir applications in interdisciplinary areas show.T he Keggin anion [CoW 12 O 40 ] 6À turns into an efficient and robust electrocatalyst upon its confinement in the welldefined void space of ZIF-8, am etal-organic framework (MOF). [H 6 CoW 12 O 40 ]@ZIF-8 is so stable to water oxidation that it retains its initial activity even after 1000 catalytic cycles. The catalyst has at urnover frequency (TOF) of 10.8 mol O 2 (mol Co) À1 s À1 ,o ne of the highest TOFs for electrocatalytic oxygen evolution at neutral pH. Controlled experiments rule out the chances of formation and participation of CoO x in this electrocatalyic water oxidation.Photosynthesis,one of the most fundamental and essential processes to sustain life on earth, works on the principle of trapping solar energy via electron-hole pair formation. [1,2] This energy is ultimately utilized in splitting of water molecules into H 2 and O 2 .W ater splitting (WS) has emerged as apromising source of clean and sustainable energy. [3] Water oxidation (WO; 2H 2 O!4H + + O 2 + 4e À ; E 0 = 1.23 V), being the bottleneck process of WS owing to its high thermodynamic potential and high overpotential h,requires an efficient and stable WO catalyst (WOC). [4,5] In last few decades, various research groups have contributed towards understanding of the process of WO and designing of robust and efficient WOCs. [1][2][3][4][5][6][7] Recently enormous efforts have been devoted to prepare first-row transition-metal-ion (particularly,c obalt)-based inexpensive WOCs. [8][9][10][11][12][13][14][15][16][17][18] Development of polyoxometalates (POMs) as WOCs came as am ajor breakthrough in this regard. [19][20][21][22][23][24][25][26][27] Thek ey structural features of POMs for POM-WOCs are their complete inorganic skeleton and the scope of fast, reversible electron transfer (resulting into fast WO kinetics). [14,28] In last few years,a long with remarkable progress in this field, questions also arose about the true catalyst species (formation and participation of CoO x as true catalyst). [28][29][30][31][32] Meanwhile,H ill, Geletii, and their coworkers [23] confirmed that their starting Co-POM compound [Co 4 (H 2 O) 2 (a-PW 9 O 34 ) 2 ] 10À was atrue molecular WO catalyst (not CoO x ). Keggin-type POMs have the general formula of [XM 12 O 40 ] nÀ (X = Co 2+ ,P 5+ ,S i 4+ ,e tc.;M= W 6+ ,M o 6+ ,e tc.) and are the most stable structural variant among all POMs. [33][34][35][36] Despite ac onsiderable development in the field of POM-WOC,n ot much attention has been paid to Keggin (as such)-WOC systems as most of them do not possess suitable WOC-active site (unless it has one or more substitution of Mb yaWO-active transition-metal ion). [28,[37][38][39] Recently,S ong et al. [37] showed K 6 [CoW 12 O 40 ]t ob ei nactive to photocatalytic WO,w hile K 7 [Co III Co II (H 2 O)W 11 O 39 ], was found to be active owing to ap eripheral Co III -aqua coordination complex. We thus made an attempt to prepare WOC from [CoW 12 ...