Electrochemical water splitting normally requires a voltage between 1.6 and 2.5 V, due to the thermodynamic requirement (1.23 V at 25 °C), ohmic resistance and overpotentials on the anode and cathode. Here, we demonstrate a new concept that successfully splits water into oxygen and hydrogen at a voltage as small as 0.8 V at room temperature (25 °C) with earth-abundance catalysts. This concept breaks the thermodynamic requirement for water splitting and provides a bright future for the hydrogen economy.