How protons can power our future energy needs

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The Conversation

The proton battery, connected to a voltmeter.

As the world embraces inherently variable renewable energy sources to tackle climate change, we will need a truly gargantuan amount of electrical energy storage.

With large electricity grids, microgrids, industrial installations and electric vehicles all running on renewables, we are likely to need a storage capacity of over 10% of annual electricity consumption – that is, more than 2,000 terawatt-hours of storage capacity worldwide as of 2014.

To put that in context, Australia’s planned Snowy 2.0 pumped hydro storage scheme would have a capacity of just 350 gigawatt-hours, or roughly 0.2% of Australia’s current electricity consumption.

Where will the batteries come from to meet this huge storage demand? Most likely from a range of different technologies, some of which are only at the research and development stage at present.

Our new research suggests that “proton batteries” – rechargeable batteries that store protons from water in a porous carbon material – could make a valuable contribution.

Not only is our new battery environmentally friendly, but it is also technically capable with further development of storing more energy for a given mass and size than currently available lithium-ion batteries – the technology used in South Australia’s giant new battery.

Potential applications for the proton battery include household storage of electricity from solar panels, as is currently done by the Tesla Powerwall.

With some modifications and scaling up, proton battery technology may also be used for medium-scale storage on electricity grids, and to power electric vehicles.

The team behind the new battery. L-R: Shahin Heidari, John Andrews, proton battery, Saeed Seif Mohammadi.

How it works

Our latest proton battery, details of which are published in the International Journal of Hydrogen Energy, is basically a hybrid between a conventional battery and a hydrogen fuel cell.

During charging, the water molecules in the battery are split, releasing protons (positively charged nuclei of hydrogen atoms). These protons then bond with the carbon in the electrode, with the help of electrons from the power supply.

In electricity supply mode, this process is reversed: the protons are released from the storage and travel back through the reversible fuel cell to generate power by reacting with oxygen from air and electrons from the external circuit, forming water once again.

Essentially, a proton battery is thus a reversible hydrogen fuel cell that stores hydrogen bonded to the carbon in its solid electrode, rather than as compressed hydrogen gas in a separate cylinder, as in a conventional hydrogen fuel cell system.

Unlike fossil fuels, the carbon used for storing hydrogen does not burn or cause emissions in the process. The carbon electrode, in effect, serves as a “rechargeable hydrocarbon” for storing energy.

What’s more, the battery can be charged and discharged at normal temperature and pressure, without any need for compressing and storing hydrogen gas. This makes it safer than other forms of hydrogen fuel.

Powering batteries with protons from water splitting also has the potential to be more economical than using lithium ions, which are made from globally scarce and geographically restricted resources.

The carbon-based material in the storage electrode can be made from abundant and cheap primary resources – even forms of coal or biomass.

Our latest advance is a crucial step towards cheap, sustainable proton batteries that can help meet our future energy needs without further damaging our already fragile environment.

The time scale to take this small-scale experimental device to commercialisation is likely to be in the order of five to ten years, depending on the level of research, development and demonstration effort expended.

Our research will now focus on further improving performance and energy density through use of atomically thin layered carbon-based materials such as graphene.

The target of a proton battery that is truly competitive with lithium-ion batteries is firmly in our sights.

Source: The ConversationReproduced with permission.  

  • Jo

    I wonder about the round trip efficiency.
    Usually the round drip efficiency in using hydrogen as storage is just around 50%, caused by so difficulties of improving energy losses in water splitting (hydrogen overvoltage).
    Another issue is oxygen. It is obviously released during water splitting and than picked up again from the air when using electricity from the cell. This means there is an entropy difference between the released oxygen (100%) and the consumed oxygen (about 20% from air). This will reduce the round trip efficiency as well.

    • john

      From the abstract.

      A ‘proton battery’ with a carbon electrode is shown to be technically feasible.

      A proton battery stores hydrogen in atomic rather than molecular gaseous form.

      The storage electrode was made from activated carbon soaked in acid.

      • Jo

        And how does this answer my questions?

    • solarguy

      I just read the abstract and it states, “in principal it will have a round trip efficientcy similar to Li-Ion. Does that answer the question.

      • Alex Hromas

        Interesting as Li-ion batteries have round trip efficiencies of 80% plus. Jo’s 50% sounds more realistic

  • Robert Comerford

    Valid questions by Jo that need to be answered.
    However any method that can store hydrogen from excess energy without requiring compression does sound useful. It’s round trip efficiency may or may not mean it is economical for the home owner.

    • Ian Porter

      The answer is it is stored by adsorption in the pore space of the (highly activated) carbon which has a surface area of >3000m2/gm, thereby avoiding the need for compression

      • Robert Comerford

        That was not the question posed Ian

      • Jo

        The low round trip efficiency of energy storage with hydrogen is mainly caused mainly caused by low efficiency of fuel cells and hydrolyser. One main reason for that is ‘overvoltage’. You have to use a much higher voltage to hydrolyse the water than you get back from the fuel cell. Decades of research to improve this significantly has not been successful.
        This has nothing to do with the compression of the gas.

        • Jo

          A bit (actually a lot) mor detail can be found here:
          If you compare the voltage of hydrolysis (about 1.8V on page 147) to the voltage of the fuel cell (less than 1V on page 151) you can see where I am coming from. The voltage difference is ‘lost’ (converted to heat) energy.

        • Ian Porter

          I am not disputing the facts you state re RTE of electrolysers and FCs. Its correct, but I am sticking with my point that compression has a lot to do with this matter. Compression storage and distribution (CSD) has everything to do with the value chain of hydrogen, and compression is by far the greatest component of this (>50% actually). Remember hydrogen has lowest energy density by volume, and highest by mass. In instances where the principle of adsorption is not used, high pressures (700Barg) are required to give you the energy density needed to compete with alternatives. The energy in compression required to get there pulls the carpet from under hydrogen value proposition.

          • Jo

            Ian you are missing the point. The round trip efficiency is well below 50%, even if the extra effort of compressing H2 has not been accounted for. So including compression, the round trip efficiency would be more lie 30% or so.

          • Ian Porter

            Not missing it, I guess a misunderstanding between us. I totally agree with you. RTE of electrolyser with FC is bad. The CSD just makes it dreadful.

  • Peter F

    While this quite exciting the storage figure seems to be way over the top. For example in Australia other than existing hydro 1 day at peak demand is almost certainly enough storage and as Jo asks, an important question is round trip efficiency

    • Alex Hromas

      This seems to be a sticking point my experience with hydrogen fuel cells is that their efficiencies are around the 35%.