Hydrogen Production and Water Desalination with On-demand Electricity Output Enabled by Electrochemical Neutralization Chemistry.

Energy-saving hydrogen production can be achieved by using renewables or decoupling the sluggish oxygen evolution reaction from overall water splitting, which still needs electricity input. We have realized hydrogen production and water desalination with on-demand electricity output via an electrochemical neutralization chemistry strategy that couples acidic hydrogen evolution and alkaline hydrazine oxidation with ionic exchange. The electrochemical neutralization cells allow efficient use of chemical energy and low-grade heat from the surroundings to output 0.81 kWh electricity per m 3 of hydrogen. Cell function can be rapidly switched to electricity output with a high peak power density up to 85.5 mW cm -2 or spontaneous hydrogen production at a high rate up to 70.1 mol h -1  m -2 without breaking cell operation or changing cell configuration. Fast water desalination is simultaneously achieved at a high salt removal rate of 56.1 mol h -1  m -2 without an external electricity supply.