Efficient　water　oxidation　remains　a　particular　challenge　in　water　splitting　that　calls　for　developing　robust　and　economic　water　oxidation　catalysts　(WOCs),　preferably　based　on　earth-abundant　transition　metals.　Herein,　we　report　a　robust　and　noble　metal-free　catalytical　system　using　BiVO4　as　an　effective　light　harvesting　material,　a　cobalt-containing　polyoxometalate　K4H1.2[Co-0.6(H2O)(0.6)SiW11.4O39.4]　(1)　as　molecular　cocatalyst,　and　NaIO3　as　a　sacrificial　electron　acceptor　for　visible-light-driven　water　oxidation　in　a　wide　pH　range　1-7.　The　combination　of　1　+　BiVO4　samples　gives　better　oxygen　evolution　activities　than　that　of　pristine　BiVO4.　A　turnover　number　(TON)　of　326.3,　apparent　quantum　efficiency　(AQE)　of　10.0%,　and　an　O-2　yield　of　21.8%　are　obtained　under　pH　4.　This　work　investigates　two　kind　different　catalytic　behaviors　for　1-cocatalyzed　visible　light　driven　water　oxidation　at　pH　1-7　media,　which　exhibits　a　pH　induced　dynamic　change　on　the　catalytic　active　species.　Catalytic　behavior,　XPS,　SEM　and　TEM　collectively　testify　that　1　remains　intact　during　photocatalytic　water　oxidation　under　pH　4-5.　Conversely,　under　pH　1-3　and　6-7,　the　heterogeneous　CoOx　originated　from　1　is　formed　on　the　BiVO4　surface,　which　is　responsible　for　the　enhancement　of　BiVO4　photocatalytic　activity.　Our　work　uncovers　the　borderline　between　homogeneous　and　heterogeneous　WOCs　using　a　cobalt-based　polyoxometalate　at　different　pH　media,　which　helps　to　the　study　of　stability　for　polyoxometalates　when　semiconducting　material　is　used　as　the　light-harvesting　material.　(C)　2020　Elsevier　Inc.　All　rights　reserved.