Solar water splitting: efficiency discussion

TL;DR

This paper reviews the current efficiency of solar water splitting, presents a case study demonstrating 10% light-to-hydrogen conversion efficiency, and reveals new insights into the oxygen evolution reaction mechanism.

Contribution

It introduces a detailed mechanism analysis of oxygen evolution and demonstrates a practical solar-to-hydrogen efficiency of 52% using simple components.

Findings

Hydrogen peroxide formation affects oxygen evolution.

Achieved 52% electrical-to-hydrogen efficiency with a simple solar cell.

Demonstrated 10% light-to-hydrogen conversion with household solar cells.

Abstract

The current state of the art in direct water splitting in photo-electrochemical cells (PECs) is presented together with: (i) a case study of water splitting using a simple solar cell with the most efficient water splitting electrodes and (ii) a detailed mechanism analysis. Detailed analysis of the energy balance and efficiency of solar hydrogen production are presented. The role of hydrogen peroxide formation as an intermediate in oxygen evolution reaction is newly revealed and explains why an oxygen evolution is not taking place at the thermodynamically expected 1.23 V potential. Solar hydrogen production with electrical-to-hydrogen conversion efficiency of 52% is demonstrated using a simple ~0.7%-efficient n-Si/Ni Schottky solar cell connected to a water electrolysis cell. This case study shows that separation of the processes of solar harvesting and electrolysis avoids photo-electrode corrosion and utilizes optimal electrodes for hydrogen and oxygen evolution reactions and achieves ~10% efficiency in light-to-hydrogen conversion with a standard 18% efficient household roof Si-solar cells.