A scientometric review of research in hydrogen storage materials

Hydrogen is a promising sustainable energy carrier for the future due to its high energetic content and no emissions, other than water vapor. However, its full deployment still requires technological advances in the renewable and cost-effective production of hydrogen, cost reduction of fuel cells and especially in the storage of hydrogen in a lightweight, compact and safe manner. One way to achieve this is by using materials in which hydrogen bonds chemically, or by adsorption. Different kinds of Hydrogen Storage Materials have been investigated, such as Metal-Organic Frameworks (MOFs), Simple Hydrides (including Magnesium Hydride, MgH₂), AB₅ Alloys, AB₂ Alloys, Carbon Nanotubes, Graphene, Borohydrides, Alanates and Ammonia Borane. Billions have been invested in Storage Materials research, resulting in tens of thousands of papers. Thus, it is challenging to track how much effort has been devoted to each materials class, by which countries, and how the field has evolved over the years. Quantitative Science and Technology Indicators, produced by applying Bibliometrics and Text Mining to scientific papers, can aid in achieving this task. In this work, we evaluated the evolution and distribution of Hydrogen Storage Materials research using this methodology. Papers in the 2000–2015 period were collected from Web of Science and processed in VantagePoint® bibliometric software. A thesaurus was elaborated relating keywords and short phrases to specific Hydrogen Storage Materials classes. The number of publications in Hydrogen Storage Materials grew markedly from 2003 to 2010, reducing the pace of growth afterwards until a plateau was reached in 2015. The most researched materials were MOFs, Simple Hydrides and Carbon-based materials. There were three typical trends in materials classes: emerging materials, developed after 2003, such as MOFs and Borohydrides; classical materials with continuous growth during the entire period, such as Simple Hydrides; and stagnant or declining materials, such as Carbon Nanotubes and AB₅ Alloys. The main publishing countries were China, countries from the European Union (EU) and the USA, followed by Japan. There is a division between countries with continued growth in recent years, such as China, and those with stagnant production after 2010, such as the EU, the USA and Japan. The results of this work, compared to a previous study in storage materials patenting by our group, and the recent launch of commercial hydrogen cars and trains and stationary hydrogen production and fuel cell solutions, indicates that although the Hydrogen Energy field as a whole is transitioning from lab and prototype stages to commercial deployment, materials-based hydrogen storage still has base technological challenges to be overcome, and therefore still needs more scientific research before large scale commercialization can be realized. The developed thesaurus is made available for refinement and future works.