The　rational　cooperation　of　sustainable　catalysts　with　suitable　light-harvesting　semiconductors　to　fabricate　photosynthetic　device/machinery　has　been　regarded　as　an　ideal　technique　to　alleviate　the　current　worldwide　energy　and　environmental　issues.　Cobalt　based　species　(e.g.,　Co-Pi,　Co3O4,　and　Co-cubene)　have　attracted　particular　attentions　because　they　are　earth-abundant,　cost-acceptable,　and　more　importantly,　it　shows　comparable　water　oxidation　activities　to　the　noble　metal　based　catalysts　(e.g.,　RuO2,　IrO2).　In　this　contribution,　we　compared　two　general　cocatalysts　modification　strategies,　based　on　the　surface　depositing　and　bulk　doping　of　ultrafine　cobalt　species　into　the　sustainable　graphitic　carbon　nitride　(g-C3N4)　polymer　networks　for　oxygenic　photosynthesis　by　splitting　water　into　oxygen,　electrons,　and　protons.　The　chemical　backbone　of　g-C3N4　does　not　alter　after　both　engineering　modifications;　however,　in　comparison　with　the　bulk　doping,　the　optical　and　electronic　properties　of　the　surface　depositing　samples　are　efficiently　promoted,　and　the　photocatalytic　water　oxidation　activities　are　increased　owing　to　much　more　exposed　active　sites,　reduced　overpotential　for　oxygen　evolution　and　the　accelerated　interface　charge　mobility.　This　paper　underlines　the　advantage　of　surface　engineering　to　establish　efficient　advanced　polymeric　composites　for　water　oxidation,　and　it　opens　new　insights　into　the　architectural　design　of　binary　hybrid　photocatalysts　with　high　reactivity　and　further　utilizations　in　the　fields　of　energy　and　environment.