Published on November 16th, 2013 | by James Ayre


Low-Cost, Corrosion-Free Water Splitter Created From Silicon And Nickel

November 16th, 2013 by  

A low-cost means of producing hydrogen fuel — one that doesn’t result in the corrosion of the materials used, and uses nothing but sunlight and water — has been created by researchers at Stanford University.

The new silicon-based water splitter — essentially just a silicon semiconductor coated in an ultrathin layer of nickel — brings the commercialization of large-scale hydrogen fuel one step closer to reality, according to the researchers involved.

This drawing shows two electrodes splitting water into oxygen (left) and hydrogen (right). The electrodes are connected via an external voltage source. The illuminated silicon electrode (left) is protected from the surrounding electrolyte by a 2-nm film of nickel and uses light energy to assist in the water-splitting process. Image Credit: Guosong Hong, Stanford University

“Solar cells only work when the sun is shining,” stated study co-author Hongjie Dai, a professor of chemistry at Stanford. “When there’s no sunlight, utilities often have to rely on electricity from conventional power plants that run on coal or natural gas.”

A better solution — according to Dai — would be to pair effective hydrogen-powered fuel cells with the solar cells.

Stanford University provides some background:

To produce clean hydrogen for fuel cells, scientists have turned to an emerging technology called water splitting. Two semiconducting electrodes are connected and placed in water. The electrodes absorb light and use the energy to split the water into its basic components, oxygen and hydrogen. The oxygen is released into the atmosphere, and the hydrogen is stored as fuel.

When energy is needed, the process is reversed. The stored hydrogen and atmospheric oxygen are combined in a fuel cell to generate electricity and pure water. The entire process is sustainable and emits no greenhouse gases. But finding a cheap way to split water has been a major challenge. Today, researchers continue searching for inexpensive materials that can be used to build water splitters efficient enough to be of practical use.

“Silicon, which is widely used in solar cells, would be an ideal, low-cost material,” stated Stanford graduate student Michael J Kenney, co-lead author of the new study. “But silicon degrades in contact with an electrolyte solution. In fact, a submerged electrode made of silicon corrodes as soon as the water-splitting reaction starts.”

To address this, the researchers have now turned to the process of coating silicon electrodes with ordinary nickel. “Nickel is corrosion-resistant,” Kenney explained. “It’s also an active oxygen-producing catalyst, and it’s earth-abundant. That makes it very attractive for this type of application.”

For the new research, a 2-nanometer-thick layer of nickel was applied onto a silicon electrode, and then partnered with another electrode and placed in a solution of water and potassium borate — light and electricity were then applied. After the application of light and electricity, the electrodes began splitting the water into oxygen and hydrogen — importantly, even after twenty-four hours the process was still continuing, with no noticeable signs of corrosion.

To further improve the process, the researchers then mixed lithium into the solution. “Remarkably, adding lithium imparted superior stability to the electrodes,” Kenney noted. “They generated hydrogen and oxygen continuously for 80 hours — more than three days — with no sign of surface corrosion.”

“Our lab has produced one of the longest lasting silicon-based photoanodes,” Dai stated. “The results suggest that an ultrathin nickel coating not only suppresses corrosion but also serves as an electrocatalyst to expedite the otherwise sluggish water-splitting reaction. Interestingly, a lithium addition to electrolytes has been used to make better nickel batteries since the Thomas Edison days. Many years later we are excited to find that it also helps to make better water-splitting devices.”

The researchers are now planning to follow this work up with efforts to further improve the stability and durability of the nickel-treated electrodes of silicon, in addition to improving the other materials used.

The new research was just published in the November 15th edition of the journal Science.

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's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.

  • Wayne Williamson

    I’m pretty sure that nickel is not “earth abundant”…ok just checked wikipedia and it is fairly abundant, kind of ranks around copper and zinc.

  • mds

    Seems to me this entire approach is flawed. I’m thinking a solar device with water in it, that you also collect hydrogen and vent oxygen from is going to be a pain to deal with. As a result, it is going to be fundamentally uneconomical and won’t scale. How are you going to keep supplying clean, pure H2O so your system won’t get fouled? How are you going to collect the H2? How are you going to prevent algae growth?

    I’m thinking regular solar panels with a separate electrolyzer would be far more practical. The other two articles (or one repeated) in and mention 15% to 25% conversion efficiency being needed for commercial viability. This is conversion efficiency from sunlight energy to H2. (Of course, I’m thinking which is it 15% or 25%? Sounds like non-sense to me if you’re going put a range of efficiency down.)

    OK several current mono-crystalline silicon PV companies have panels with 20% efficiency. Let’s say we have a 70% efficient electrolyzer. (Is 60% more realistic based on what is available now?) That would mean our overall efficiency from sunlight to H2 would be 0.70 x 0.20 = 0.14 => 14% efficiency, close to the 15% claimed. This is why hydrogen energy storage is heating up in the market place recently. No… Wait… It’s not? No, it’s not competitive with batteries for grid storage. Read these: “MIT’s Ambri
    Opens Factory” – November 2013 – October 2013
    “AE12 Battery Module for Stationary, Long-Duration Energy Storage” – November 2013
    “Eos Energy Storage Launches Megawatt-Scale Manufacturing In New York”

    Also, Lithium batteries for use in EVs/E-REVs are getting better: – June 2013
    “ZSW develops process for Li-ion batteries with extended cycle life; 10,000 charge cycles” l “A123
    Venture Technologies to collaborate with SolidEnergy on safer, high-energy battery chemistry; potentially up to ~800 Wh/kg” – October 2013 – February 2012
    “Envia Systems hits 400 Wh/kg target with Li-ion cells; could lower Li-ion cost to $180/kWh”
    I don’t see where hydrogen energy storage is practical yet. Maybe it never will be?

    • Bob_Wallace

      Every time I see an article about hydrogen as a fuel/storage technology I am reminded of the graphic I’m posting at the bottom of this comment.

      Getting from electricity -> hydrogen -> electricity is a very inefficient process, or at least it has been. Unless the process is made much more efficient I can’t see any role for H2, or a fuel derived from it, except as possible deep storage.

      That’s assuming large scale storage would be cheap.

      • JamesWimberley

        Bob must be right that generating electricity with hydrogen produced by renewable electricity is absurd, except for rarely used deep backup in a 100% renewables scenario. In practice this would involve running gas turbines we already have. The competition is other forms of storage.

        The most plausible uses for synfuels are in aviation and shipping, and some industrial processes like steel and cement-making. SFIK we don’t yet have good technical alternatives to combustion here.

        There are pilot power-to-gas plants in Germany, some using the Sabatier reaction to create methane rather than hydrogen.

        • Marion Meads

          Slight modification of current ICE, hydrogen can be used as fuel or fuel supplement. This would allow re-using the existing infrastructure of agricultural machineries for example, as it would be expensive to purchase new machineries that uses battery power alone, such as the massive tractors and combines at the moment.

          • Bob_Wallace

            Farming is a pretty harsh environment and hydrogen is a very leaky fuel.

            I think some form of biofuel has a future for those applications where electricity/batteries would not work well. But it we need a renewable electricity generated fuel I suspect it would be better to turn the hydrogen into something a bit easier to contain.

          • Marion Meads

            Solar hydrogen has way overall better efficiency than the best biofuel currently there is. For starters, the average yield of biofuel is less than 1% of solar energy, with majority of the sun’s energy used in evaporating water from plants. Then you have conversion losses from sugars or cellulose to biofuel, and also the energy used for processing, reforming and refining.

            Agree that storing hydrogen can be problematic but researchers have been working hard on that also.

  • Marion

    Report of Kevin Bullis at MIT Tech Review talked about 2 nanometer coating of Zinc over Silicon to achieve non-corrosive properties. Nathan here reports coating of Nickel over Sili

    So who got the report right?

    • mds

      Comment from “bigstack89” at end of your technology review article:
      “Interesting article. One issue is that it is using nickel not zinc if the article is:”
      2 to 1 it is nickel and Nathan is correct.
      Comment there by “yoatman” is also interesting.

    • JamesWimberley

      The Stanford press release and the Science article both say nickel, so Bullis (unusually) got it wrong.

  • mds

    Please read this section in Wikipedia:
    “The energy efficiency of water electrolysis varies widely. Some report 50–80%. These values refer only to the efficiency of converting electrical energy into hydrogen’s chemical energy. If one considers simply the electrical energy input to an electrolyser and the enthalpy of combustion of the H2 product (therefore the energy input and the energy output of the system), then voltage efficiency (HHV) of greater than 82% is achievable[1] (using platinum catalysts and PEM technology, with H2 production occurring at 1.55V, with ideal Faraday efficiency being achieved).”
    So it’s not just the durability of the electrodes, it is also the efficiency of conversion of electricity to H2 that effects the economics of H20 to H2 conversion for energy storage.
    What is the efficiency of H2 production with the durable electrodes this team has developed?
    (It is generally true for all energy storage that the input-to-output efficiency is a significant factor in the economic viability of the storage approach used.)

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