Catalyst-free hydrogen evolution of Si photocathode by thermovoltage-driven solar water splitting

AbstractAn externally biased overpotential is normally required for photoelectrochemically cleaving water molecules. Moreover, very few semiconductors exhibit the necessary performance for the efficient transfer of photon energy to the binding electrons of water molecules unless a suitable catalyst is present. Here, we present a catalyst-free photoelectrochemical (PEC) cell electrically coupled in series with a thermoelectric device, which is capable of utilizing the full solar spectrum by synergistically collecting photon and phonon energies. Thermodynamic overpotentials originally required for the PEC reaction were spontaneously offset by the thermovoltage, which adjusts the Fermi level of a counter-electrode. Using a catalyst-free Si photocathode of unbiased conditions, we achieved a photon-to-current efficiency of ∼20% at an 56 °C temperature gradient by harnessing only solar energy