Considering the industrial production of hydrogen, and using current best processes for water electrolysis (PEM or alkaline electrolysis) which have an effective electrical efficiency of 70–80%, producing 1 kg of hydrogen (which has a specific energy of 143 MJ/kg) requires 50–55 kW⋅h (180–200 MJ) of electricity.

Disadvantages of electrolysis of water. it takes a lot of energy to separate the water into hydrogen and oxygen. if you burn fossil fuels to create the energy for electrolysis water the process produce lots of emission. of CO2.

In this process, water is split into hydrogen and oxygen using an electrolyte solution, typically potassium hydroxide (KOH) or sodium hydroxide (NaOH). The electrolyte solution conducts electricity between two electrodes (anode and cathode), facilitating the reaction that generates hydrogen gas.

A green and sustainable route for H2 production to support this technology is water electrolysis using renewable or excess electricity; however, it is an energetically uphill process involving the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode.