Hydrogen fuel from water almost within our grasp
A cheap hydrogen generator that relies on a nickel nanoparticle may be the game-changer we have been waiting for. Cathal O'Connell reports.
Next year the first wave of commercial hydrogen-fuelled cars from Toyota and Hyundai will hit the market, promising a future of green, emission-free vehicles for all. The problem is that most of the world’s hydrogen is made from natural gas in a process that releases about 400 million tonnes of CO2 into the atmosphere annually – more than 1% of total man-made emissions. Water offers a perfectly clean alternative source. But making hydrogen from water is prohibitively expensive.
Now a team of scientists led by Hongjie Dai at Stanford University has found a way to drive down the cost. The breakthough is the catalyst – a “Malteser-shaped” nickel nanoparticle. Their method was published in Nature Communications in August. “The device could be powered by a single AAA battery,” says Ming Gong, a PhD student and lead author of the research.
Splitting water using a 1.5 volt battery has been done before using platinum, says Doug MacFarlane, an electrochemistry expert at Monash University. “The main achievement is to make a catalyst that can be produced cheaply.”
The standard way to split hydrogen from water is to zap it with an electric current. That sends the hydrogen bubbling out, but it takes a lot of electricity. Coating the electrodes with a catalyst lowers the energy required, but by far the most effective catalyst, platinum, is hugely expensive – literally worth more than its weight in gold.
So Gong set out to see if a less expensive metal, like nickel, could be tweaked to do the same trick. Previous work had shown that making metal catalysts in nanoparticle form can increase their efficiency by exposing more active surface. So Gong started to develop nickel nanoparticles and to test them for catalysis. The breakthrough came when he synthesized a new kind of nanoparticle with a nickel core and a nickel oxide shell. When he tested its efficiency he was amazed to find that it was nearly as effective as platinum.
The secret to the new material’s efficiency is still unknown. But when the team took a closer look at the nanoparticles they found that some of the nickel oxide shells had unusual defects which exposed the nickel core. The team thinks the catalysis action might happen at this exposed interface where the nickel and nickel oxide meet. One problem is the material degrades after several days' use. “The next step will be improving the durability of the catalysts from days to more than weeks,” says Gong.
MacFarlane says generating hydrogen could help make green power more reliable. Power generation by a wind farm or solar farm can be as changeable as the weather. Sometimes too much electricity is generated than can be used at a particular moment. By hooking up a wind turbine or solar panel to a water-splitter excess energy could be stored as hydrogen, using it to generate electricity for the grid as needed.