| Electrolytic efficiency | $η_{V}=\frac{E_{O_2}-E_{H_2}}{E} \times 100\%$ | The ratio of effective voltage of electrolysis to total voltage | The electrolytic efficiency described by balancing electromotive force and electrolytic voltage is a common way to measure the electrolytic efficiency of hydrogen production system |
| Faraday efficiency | $\eta_{\Delta G}=\frac{\Delta G}{\Delta G+Losses}=\frac{E_{\Delta G}}{E}$ | The ratio of the theoretical energy of electrolytic water to the actual input energy | $\eta_{25 ℃}=\frac{1.23V}{E}$ |
| Thermal efficiency | $\eta_{\Delta H}=\frac{\Delta H}{\Delta G+Losses}=\frac{E_{\Delta H}}{E}$ | The proportion of the actual electrolytic energy that is input to maintain heat balance | $\eta_{25 ℃}=\frac{1.48V}{E}$,1.48 is the electrolytic voltage when thermoneutral, and the thermal efficiency is 100% when E is equal to 1.48. The thermal efficiency can be higher than 100% when external heating is provided |
| Hydrogen production efficiency | $\eta_{H_2}=\frac{283.8(kJ)}{Uit}$ | The ratio of the energy generated by 1g of hydrogen to the total energy input | The calorific value of hydrogen is 283.8kJ/g, U is the electrolytic voltage, i is the current, and t is the time required to produce 1g hydrogen |
| Net efficiency | $\eta_{Loss}=1=\frac{E_{Loss}}{E_{input}}$ | 1 minus the energy lost as a percentage of the total energy | $E_{Loss}=\eta+iR_{cell}$ |
