Most research in the field of carbon-friendly solar hydrogen splitting is also bent on finding a substitute for today’s expensive platinum catalyst, which keeps hydrogen fuel cells prohibitively expensive. The options range from Duke University’s idea of producing hydrogen from rooftop solar collectors—glass vacuum tubes filled with water and methanol and catalytic nanoparticles—to Nocera’s cheap cobalt and nickel catalysts.

But in addition to using the future’s plentiful sunlight—and cheap and abundant silicon and zinc oxide nanowires—Wang’s breakthrough also involves a nanoscale structural change in how the sunlight is actually absorbed. This structure is key in improving the efficiency of the process.

image via Shutterstock

The trees’ vertical structure and branches are keys to capturing the maximum amount of solar energy.

That’s because the vertical structure of trees grabs and adsorbs light while flat surfaces simply reflect it, Wang said, adding that it is also similar to retinal photoreceptor cells in the human eye. In images of Earth from space, light reflects off flat surfaces such as the ocean or deserts, while forests appear darker.

The vertical branch structure also maximizes hydrogen gas output, said Sun. For example, on the flat, wide surface of a pot of boiling water, bubbles must become large to come to the surface. In the nanotree structure, very small gas bubbles of hydrogen can be extracted much faster, enhancing the surface area by as much as 400,000 times.

Once cheap enough, widespread uses of hydrogen fuel cells would make storing energy much cheaper, in buildings, on the grid, and in vehicles—ranging from cheaper fuel-cell vehicles at military installations on the gas-dependent island of Hawaii—to possibly the most adorable single occupancy vehicle ever designed.

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