Earth-abundant, active and stable water splitting electrocatalysts operating in the same electrolyte at all pH values is important for many renewable energy conversion processes. We report here the first carbon nanomaterials-based metal-free water splitting electrocatalyst. The nitrogen, phosphorus and oxygen tri-doped porous graphite carbon@oxidized carbon cloth (ONPPGC/OCC) electrocatalyst can be prepared by a simple cost-effective method using aniline, phytic acid and OCC as precursors. Being a robust integrated three-dimensional porous bifunctional electrode, ONPPGC/OCC enables a high-performance basic water electrolyzer with 10 mA cm⁻² at a cell voltage of 1.66 V. Additionally, this electrode offers excellent catalytic performance and durability under both neutral and acidic conditions.