The discovery of new materials is a paramount endeavor in the pursuit to transition our global energy infrastructure from fossil to renewable power. Surprisingly, it has been revealed that this paradigm can be turned upside down with the rediscovery of old materials that enable large-scale electricity storage and hydrogen generation — two foundations of the energy transition
Past editor of the journal Nature, Philip Ball, one said, “A breakthrough is a discovery pregnant with promise, and then the hard graft begins”. Any scientist who has experienced a breakthrough — either by design or by chance — knows the rush of discovery and the exhilaration of sharing this knew knowledge with the community. But this is just the first step on the often decades-long road to technological practicality.
Naturally, one would like to initiate and complete the cycle of discovery-to-technology as fast as possible. The alure of accelerating the process, whether by human ingenuity, luck, or artificial intelligence, to be first to the finishing line, by any means, is irresistible.
But the trick is that sometimes materials needed to solve big and important problems don’t have to be discovered; they exist as hidden gems waiting to be rediscovered. Two such recent cases of old materials look like they have a high probability of impacting large-scale, low-cost grid-storage of electricity and production of golden hydrogen.
Examples of this concept of materials rediscovery is metallic iron and a semiconductor called silicon carbide, both well-documented, abundant, low-cost, and non-toxic solids. While being “old” materials, they have recently allowed two spin-off companies to scale and evaluate the performance metrics of a practical iron-air battery, and a silicon carbide solar water splitter, respectively.
Grid-scale electricity storage and hydrogen from sunlight
The iron-air battery is being developed by the company, Form Energy, targeting year-round grid electricity storage. The device operates on an iron-iron oxide redox cycle, it is fully renewable, resilient, cost-effective, and it can steadfastly store large amounts of electricity for many days.
The first commercial product has electricity storage capacity of 100 hours with an overall system cost that competes with legacy power plants. While its heavy mass and slow cycling time makes it unsuitable for electric vehicles, its high capacity makes it ideal for grid-scale electricity storage.
The first high-volume iron-air battery manufacturing facility of Form Energy is located in West Virginia, USA. They are rejuvenating an existing steel plant projected to employ more than 750 people and will manufacture 500 megawatts of batteries per year under full operating capacity.
The yellow silicon carbide semiconductor for producing hydrogen from water and sunlight is also now being manufactured on a large scale by the Yellow SiC group. To function well for water splitting to hydrogen, the material must have very high purity (less than 1 ppm impurities) and exist as the cubic polymorphic form of silicon carbide.
The electronic band properties of this kind of silicon carbide are key to success. Specifically, the electronic band gap is 2.36eV. This energy is close to the ideal band gap of 2.03eV that maximizes the light-assisted water splitting efficiency of a single semiconductor material. Furthermore, the electronic band structure of this silicon carbide perfectly straddles the oxidation and reduction potentials of water, a condition necessary required to produce oxygen and hydrogen, respectively, making notably making it ideal for solar water splitting in the absence of an external voltage bias.
This makes this “old” material the perfect candidate for achieving unassisted (electricity-free) photocatalytic production of hydrogen from water and sunlight. While few catalyst and device details are available, it seems that the solar hydrogen photocatalytic production module is a simple, wireless layer structure comprised of a thin film of yellow silicon carbide acting as the positive anode, where the water forms oxygen and protons. The silicon carbide is interfaced with a negative metal cathode where the electrons and the protons produced at the silicon carbide come together to produce hydrogen. To complete the water splitting reaction the protons must diffuse from anode and cathode, a task that appears to be facilitated by a membrane that conducts protons.
This simple device is earmarked for rooftop solar hydrogen factories. In operation it enables electricity-free stable production of the greenest form of hydrogen, called golden hydrogen, directly from water and sunlight. It has an estimated cost of $0.75-2.00/kg hydrogen depending on geographic location and how many hours of the day the sun shines. These costs seem to make yellow silicon carbide the material of choice to produce golden hydrogen, when compared to green hydrogen from electrolysis of water using renewable electrical energy cost-rated in 2022 at $.4.48-6.71/kg.
The moral to the story is not to replace the discovery of new materials in the search to develop sustainable energy technologies to help solve today’s climate change problems. Rather the point is to be constantly alert to the possibility that plenty of old materials remain to be rediscovered and accomplish or better the same objectives.
Written by: Geoffrey Ozin
Solar Fuels Group, University of Toronto, Email: [email protected], Website: www.solarfuels.utoronto.ca
Feature image credit: Javier Miranda on Unsplash
