Vattensplitting

Vattensplitting, or water splitting, is the chemical process of decomposing water into hydrogen and oxygen using energy input. The overall reaction is 2 H2O → 2 H2 + O2. In practice, the process requires energy input greater than the thermodynamic minimum of about 1.23 V due to overpotential and system losses. It is a central concept in hydrogen production and in strategies for storing energy as chemical fuel.

Several methods are used to achieve vattensplitting. Electrolysis uses electricity to drive the reaction, with common technologies including alkaline electrolysis, proton-exchange membrane (PEM) electrolysis, and solid-oxide electrolysis (SOEC) operated at high temperatures. Photochemical, photoelectrochemical, and photocatalytic approaches use light to drive water splitting, sometimes without external electricity. Thermolysis at high temperatures can split water with heat supplied from concentrated solar or fossil sources, typically in combination with catalysts.

Electrolysis details: Anode catalyzes oxygen evolution (OER) while the cathode performs hydrogen evolution (HER). Electrolyte choice affects efficiency and durability; typical systems use alkaline solutions or solid membranes. Energy efficiency, faradaic efficiency, and overall system efficiency depend on electrode materials, overpotentials, and operating conditions. In renewable-energy contexts, "green hydrogen" refers to hydrogen produced by splitting water with electricity from renewables.

Applications include industrial hydrogen supply, fuel for transportation, and energy storage for power systems. When integrated with intermittent renewables, vattensplitting can help balance the grid by converting surplus electricity into hydrogen, which can be stored or reconverted to electricity or used as chemical feedstock.

Challenges include high capital costs, durability of catalysts and membranes, and purity and safety considerations. Hydrogen's low energy density by volume requires robust storage and appropriate safety measures. Research aims to reduce material costs, improve efficiency, and enable large-scale, low-emission production.