Maximizing Solar Hydrogen Fuel Production

A research team from Switzerland has developed and demonstrated a new photo-electrochemical device that works in tandem with a solar concentrator to maximize hydrogen fuel production while minimizing the need for expensive photoabsorber and electrocatalyst materials. During concept demonstrations, the scientists reportedly observed record-level current densities and high energy-conversion rates. The concept may help make environmentally friendly hydrogen fuel derived from solar irradiation a more practical alternative to fossil fuels (Nature Energy, doi: 10.1038/s41560-019-0373-7)

The researchers have set up a seven-foot mirrored dish on the Ecole Polytechnique Fédérale de Lausanne’s (EPFL) campus to field-test the device, which they will monitor in real time with a novel open-source software interface.

The promise of clean hydrogen fuel

Solar energy collected by photovoltaic (PV) systems can power a chemical reaction that splits water into oxygen (O2) and hydrogen (H2) molecules. The hydrogen molecules can be used as fuel immediately or stored and converted to electricity as needed. And since the only outputs from the process are oxygen, hydrogen and leftover water, solar hydrogen is considered a pollution-free fuel.

PV systems have been around since the 1970s, but clean hydrogen fuel has yet to be made reliably and affordably on a large scale. One reason is that PV systems require expensive and rare materials in both the photoabsorber layer that collects irradiation from the sun and the electrocatalyst layer that powers the chemical reaction. The EPFL team—led by Sophia Haussener, who helms the Laboratory of Renewable Energy Science and Engineering (LRESE)—may have found a way to scale up solar-hydrogen fuel production while keeping materials costs down.

One part of the proposed solution is a new photo-electrochemical device. This device employs a thin layer of running water to improve the photoabsorber layer’s performance by removing some of the intense heat it receives from direct sunlight and transferring it to the electrocatalyst layer, to help power the chemical reaction that creates solar hydrogen fuel. When combined with a solar concentrator, this enhanced photo-electrochemical system can, say the researchers, generate more hydrogen fuel with smaller and therefore less expensive components.

In addition to being efficient, Haussener and her colleagues say that the smaller-sized systems are durable. They estimate that the system’s components can operate without replacement parts for about four years, and could last up to 20 years with regular maintenance at four-year intervals.

Testing lab- and field-scale systems

The team used LRESE’s high-flux solar simulator to demonstrate its device in the lab. During these technology demonstrations, the researchers report observing a 17 percent solar-to-hydrogen conversion efficiency, an output power of 27W and “unprecedented” electrochemical and PV current densities of 0.88 A cm-2 and 6.04 A cm-2.

These promising results prompted the team to scale-up the system for field studies. The researchers are now testing a seven-meter parabolic mirror outfitted with a solar concentrator that can amplify the sun’s irradiation by a factor of 1,000. In a press release, Haussener says that the field-scale system can generate up to 1 kg of hydrogen per day, which is enough to fuel a hydrogen-powered car for 150 km.

With a spin-off company called SoHHytec, Haussener and her colleagues hope to take their solar-concentrator technology from EPFL to industry. The researchers have also developed open-source software programs that anyone can use to help them create, compare and assess their own low-cost hydrogen-fuel-producing photo-electrochemical systems.

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