Researchers at Stanford University have demonstrated solar water splitting by photovoltaic-electrolysis with a solar-to-hydrogen efficiency of more than 30%. The work surpassed the previous efficiency record of 24.4%.

Stanford University researchers led the work.Stanford University researchers led the work.The system consists of two polymer electrolyte membrane electrolyzers in series with one InGaP/GaAs/GaInNAsSb triple-junction solar cell, which produces a large-enough voltage to drive both electrolyzers with no additional energy input. The solar concentration is adjusted so that the maximum power point of the photovoltaic is well matched to the operating capacity of the electrolyzers to optimize system efficiency. The results, the researchers say, demonstrate the potential of photovoltaic-electrolysis systems for cost-effective solar energy storage.

Each material in the triple-junction cell is tuned to capture blue, green, or red light, respectively. Through this precision, the cells convert 39% of incoming solar energy into electricity. That compares with roughly 20% for silicon-based, single-junction solar cells commonly deployed on rooftops.

While most photovoltaic-powered water-splitting reactions use a single electrolysis device, the researchers combined two identical electrolysis devices in such a manner to produce twice as much hydrogen, making use of their higher-efficiency solar cells.

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