Photocatalytic　water　splitting　is　a　promising　and　clean　way　to　mimic　plant　photosynthesis　in　a　sustainable　manner.　Improvements　of　the　quantum　efficiency　and　optical　absorption　in　the　relevant　range　are　necessary　steps　to　approach　practicality.　Herein,　we　reported　that　these　issues　can　be　readily　addressed　when　5-aminotetrazole,　a　monomer　with　high　nitrogen　content,　is　used　for　the　synthesis　of　carbon　nitride.　The　molten　salt　mixture　NaCl/KCl　is　used　as　a　high-temperature　solvent　to　tailor　the　grain　boundary　structure　and　chemistry.　Visible　light　quantum　efficiency　for　H　2　production　of　0.65　could　be　obtained　in　the　presence　of　K　2　HPO　4　as　a　double　layer　modifier.　This　value　is　very　high,　considering　that　this　number　depends　on　light　to　charge　couple　conversion,　charge　localization,　as　well　as　a　successful　oxidation　and　reduction　reaction.　©　2019　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim