(352g) H2 Production Via Photovoltaic-Electrolysis with over 30% Solar-to-Hydrogen Efficiency

Benck, J. D., Massachusetts Institute of Technology
Seitz, L. C., Michigan State University
Ng, J. W. D., Stanford University
Harris, J., Stanford University
Jaramillo, T. F., Stanford University
Solar water splitting is a promising technique for producing clean, renewable H2. Currently, no solar water splitting devices are economically competitive with alternative technologies such as steam methane reforming. A great deal of effort has been invested into developing devices with high solar to hydrogen (STH) efficiency, because modeling studies have predicted that device efficiency is a primary factor that affects the overall H2 cost.

We report a photovoltaic-electrolysis system with the highest STH efficiency for any water splitting technology reported to date, to the best of our knowledge. This system consists of two polymer electrolyte membrane electrolyzers in series with one triple-junction InGaP/GaAs/GaInAsSb photovoltaic cell, which produces a high enough voltage to drive both electrolyzers with no additional energy input. The solar concentration is is adjusted such that the maximum power point of the photovoltaic is well matched to the operating capacity of the electrolysers to optimize the system efficiency.

Our system achieves a 48 hour average STH efficiency of 30%. This high efficiency demonstrates that photovoltaic-electrolysis systems are a promising solution for cost-effective solar energy storage. We will discuss the implications of these results for the comparitive advantages and disadvantages of competing electrochemical H2 production technologies and suggest directions for further research in this area.