There is ever-increasing concern about fossil fuel induced climate change, which was brought to the fore once again at the recent COP28 summit in Dubai. As a result, there is significant interest in alternative fuel sources that can assist with the shift away from fossil fuels and towards net zero targets. In this article, we take a look at the latest technological developments in the field of hydrogen storage and discuss some of the issues concerning patents in this field.
Hydrogen as a fuel
Hydrogen is attractive as a fuel because its combustion or reaction with oxygen in a fuel cell releases energy without emitting greenhouse gases, since the only waste product is water. Hydrogen also has the highest gravimetric density (energy density per unit mass) of any fuel at around 120 MJ/kg, although it suffers from a very low volumetric density (energy density per unit volume), which makes transportation and storage of hydrogen in gaseous form difficult and expensive.
Hydrogen gas has found some commercial applications as a fuel, such as the Coradia iLint trains in service in Germany which store compressed hydrogen in a tank on the roof of the train and feed it to a fuel cell to generate energy. However, there are high safety, regulatory and infrastructure hurdles to overcome whenever hydrogen gas is used in this sort of way. Materials that can store hydrogen in the solid state and release it in situ when needed are therefore an attractive solution because they remove the need to transport and store gaseous hydrogen. Such materials could potentially be used in power stations, vehicles and portable electronic devices such as mobile phones.
Hydrogen storage technology
Solid state hydrogen storage materials have been the subject of intensive research for several decades and government authorities in many countries including the US, Europe and Japan have set ambitious targets for their development in recent years.
Developing materials that can store an appreciable amount of hydrogen reversibly without having to use high pressure and/or low temperature is a significant challenge. Nevertheless, a number of promising solid state hydrogen storage materials have been developed and several have found commercial applications. Some of the most exciting classes of these materials are discussed below.
Metal hydrides – metal hydrides are compounds formed between metals and hydrogen, encompassing molecular hydrides and hydrogen stored in intermetallic compounds or alloys. Many hydrogen storage alloys have been developed, with the most interest being devoted to AB5 systems (where A is a rare earth metal and B is a transition metal, usually nickel) and AB2 systems (where A is a rare earth metal, titanium, zirconium or hafnium and B is a transition or non-transition metal).
Magnesium hydride (MgH2) is the most widely studied metal hydride of late and is an attractive material because magnesium is very abundant, light and cheap. However, pure MgH2 is very stable and hydrogenation/dehydrogenation is very slow even at high temperatures. Innovative techniques have been developed to improve performance, such as forming MgH2 nanoparticles by milling, nanoconfinement of MgH2 in porous materials and doping MgH2 with transition metal catalysts.
A number of companies have commercialised metal hydride-based hydrogen storage materials, including Ergenics Corp. and Hydrogen Components, Inc. in the US, GfE, Heliocentris and IFAM in Germany, and Santoku Corporation, Japan Steel Works and Japan Metals & Chemicals in Japan.
Carbonaceous materials – carbon takes many forms, including fullerenes, carbon nanotubes (CNTs), activated carbon, graphene, graphidyne (GDY) and graphite. Although pure carbon nanomaterials are not suitable for hydrogen storage, carbon supports can be readily functionalised to form hydrogen storage materials that store hydrogen by physisorption or chemisorption. Many doped carbon materials have shown promise, including nitrogen-doped activated carbon, lithium-doped graphene and boron-doped graphidyne. These systems are typically decorated with metal nanoparticles to increase hydrogen storage capacity.
Another exciting class of carbon-based hydrogen storage materials is Liquid Organic Hydrogen Carriers (LOHCs), such as those developed by Umicore. In these systems, hydrogen is absorbed onto a liquid organic carrier using a hydrogenation catalyst to form a stable molecule such as cyclohexane or decalin. The liquid substance can be transported to fuel stations similarly to petrol or diesel, filled into a vehicle and dehydrogenated onboard using a dehydrogenation catalyst to release hydrogen as a fuel.
Metal-organic frameworks (MOFs) – MOFs are extended porous structures made from metal ions and organic linkers that have been investigated as hydrogen storage materials for nearly 25 years. They are attractive because of their high gravimetric density; hydrogen storage of up to 15 wt% has been achieved, but only at low temperatures (77 K) and high pressures. The weak interaction between hydrogen and MOFs means that only up to 1 wt% hydrogen can typically be stored at room temperature, although these systems do have the benefit of fast charge and discharge. AI-assisted computational methods may assist in finding more optimal MOFs in the near future.
Patent considerations
A report published earlier this year by the International Energy Agency (IEA) and the European Patent Office (EPO) provided detailed analysis of patent activity in the hydrogen technology field. The report showed that patent applications for hydrogen-related technologies increased steadily from 2001-2020, with Europe and Japan the leading centres of innovation, being responsible between them for more than half the patent filings in this area from 2011-2020. More than half of the $10 bn of venture capital investment into hydrogen firms between 2011-2020 went to start-ups with patents and more than 80% of late-stage investment in hydrogen start-ups in this period went to companies that had already filed a patent application to hydrogen technologies. This underlines the crucial role that patents play in driving innovation and investment in this field.
Patent offices around the world have introduced incentives for the filing of cleantech patent applications, including those relating to hydrogen-related innovations. The UKIPO offers accelerated processing under its Green Channel program for applications in this field, with the USPTO offering a similar program under its Climate Change Mitigation Pilot Program, which was expanded earlier this year specifically to cover patent applications that relate to reduction or prevention of greenhouse gas emissions. Expedited examination of such applications is also available in other major jurisdictions, including China, Canada and Australia.
The drafting of patents to protect new hydrogen storage materials requires careful characterisation and definition of the nature of the material, and there are many potential pitfalls to avoid. The definition of alloys in patents can be particularly challenging, as discussed in one of our previous articles, and the strict way that claims to alloys are analysed by the EPO means that it is vital to give careful thought to how to define these materials in the claims in order to maximise the likelihood of robust patent protection, especially in Europe. Moreover, any patent applications directed to materials defined by parameters such as pore size or surface area also require careful drafting, especially in view of the stringent requirements at the EPO for comprehensive definitions of the methods used to measure parameters recited in claims. Finally, some materials whose structure can be difficult to define accurately may be more appropriately protected with reference to how they are made, for instance using “product-by-process” claims. However, such claims can be challenging to obtain and, again, careful drafting is needed to satisfy the requirements of the patent offices, particularly the EPO.
The Chemistry team at Carpmaels has significant and relevant expertise in this area, with a group of experienced attorneys that have PhDs in inorganic or organometallic chemistry. And with one of the largest and most successful opposition practices in Europe, we have a deep understanding of the pitfalls which await poorly drafted patents in this complex area. We are therefore well placed to advise how best to obtain comprehensive and commercially useful patent protection for hydrogen storage materials and other hydrogen-related technologies.
