Enabling Unprecedented Ultra‐Efficient Practical Direct Seawater Splitting by Finely‐Tuned Catalyst Environment via Thermo‐Hydrodynamic Modulation

Abstract Direct sea water splitting as asource of clean renewable energy is indeed a holy grail and necessitates the invention of unprecedented avenues. Toward this goal, for the first time, the effect of thermo‐hydrodynamic processes modulation (electrolyte flow and heating) on water splitting reactions, through the controlling of the nanocatalyst surface environment, is studied thoroughly. A catenated sulphur type‐nickel polysulphide‐based single crystalline, high surface area 3D electrocatalyst (NiS 2 p S x surface ), with surface‐enriched oxygen evolution reaction (OER, Ni 3+ ) and hydrogen evolution reaction (HER, p S n 2− ) catalyzing species, is prepared by a single‐step process. Thermo‐hydrodynamic processes‐induced electrochemical analysis demonstrates a dramatic improvement in the electrocatalytic performance of the catalyst, by both flow and temperature modulation. Decoupling contributions from the electrolyte and electrodes heating demonstrate an intrinsic electrode property influence on the overall temperature‐dependent electrochemical performance. Furthermore, a chlorine‐phobic behavior of the NiS 2 p S x surface catalyst is observed, even at 80 °C, for direct seawater oxidation, confirming the electrocatalyst potential for direct seawater splitting. Notably, a cell voltage of 1.39 V (at 10 mA cm −2 ), reaching industrially practical large‐scale of >500 mA cm −2 is observed for additive‐free direct seawater splitting, which is the lowest reported cell voltage to date, even for alkaline additive‐based electrolysers. Consequently, an alternative approach for direct seawater splitting is realized and can be universally extended to any present‐day electrocatalyst platform.