This review focuses on key aspects of the thermal decomposition of multinary or mixed hydride materials, with a particular emphasis on the rational control and chemical tuning of the strategically important thermal decomposition temperature of such hydrides, Tdec. An attempt is also made to predict the thermal stability of as-yet unknown, elusive or even unknown hydrides. The future of a particularly promising class of materials for hydrogen storage, namely the catalytically enhanced complex metal hydrides, is discussed. The predictions are supported by thermodynamics considerations, calculations derived from molecular orbital (MO) theory and backed up by simple chemical insights and intuition.

Thermal decomposition of the non-interstitial hydrides for the storage and production of hydrogen.

Hydrogen is a promising energy carrier in future energy systems. However, storage of hydrogen is a substantial challenge, especially for applications in vehicles with fuel cells that use proton-exchange membranes (PEMs). Different methods for hydrogen storage are discussed, including high-pressure and cryogenic-liquid storage, adsorptive storage on high-surface-area adsorbents, chemical storage in metal hydrides and complex hydrides, and storage in boranes. For the latter chemical solutions, reversible options and hydrolytic release of hydrogen with off-board regeneration are both possible. Reforming of liquid hydrogen-containing compounds is also a possible means of hydrogen generation. The advantages and disadvantages of the different systems are compared.

Chemical and Physical Solutions for Hydrogen Storage

The number of research reports published in recent years on electrochemical water splitting for hydrogen generation is higher than for many other fields of energy research. In fact, electrochemical water splitting, which is conventionally known as water electrolysis, has the potential to meet primary energy requirements in the near future when coal and hydrocarbons are completely consumed. Due to the sudden and exponentially increasing attention on this field, many researchers across the world, including our group, have been exerting immense efforts to improve the electrocatalytic properties of the materials that catalyze the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode, aided by the recent revolutionary discovery of nanomaterials. However, the pressure on the researchers to publish their findings rapidly has caused them to make many unnoticed and unintentional errors, which is mainly due to lack of clear insight on the activity parameters. In this perspective, we have discussed the use and validity of ten important parameters, namely overpotential at a defined current density, iR-corrected overpotential at a defined current density, Tafel slope, exchange current density (j0), mass activity, specific activity, faradaic efficiency (FE), turnover frequency (TOF), electrochemically active surface area (ECSA) and measurement of double layer capacitance (Cdl) for different electrocatalytic materials that are frequently employed in both OER and HER. Experimental results have also been provided in support of our discussions wherever required. Using our critical assessments of the activity parameters of water splitting electrocatalysis, researchers can ensure precision and correctness when presenting their data regarding the activity of an electrocatalyst.

Precision and correctness in the evaluation of electrocatalytic water splitting: revisiting activity parameters with a critical assessment

In the search for future energy supplies, the application of hydrogen as an energy carrier is seen as a prospective issue. However, the implementation of a hydrogen economy is suffering from several unsolved problems. Particularly challenging is the storage of appropriate amounts of hydrogen. In this context one of the promising hydrogen storage techniques relies on liquid-phase chemical hydrogen storage materials, in particular, aqueous sodium borohydride, ammonia borane, hydrazine, hydrazine borane and formic acid. The use of these materials in hydrogen storage provides high gravimetric and volumetric hydrogen densities, low potential risk, and low capital investment because it is largely compatible with the current transport infrastructure. In this review, we survey the research progresses in hydrogen generation from these liquid-phase chemical hydrogen storage materials and their regeneration.

Liquid-phase chemical hydrogen storage materials

Light metal hydrides and complex hydrides for hydrogen storage.

Hydrogen generation using sodium borohydride solution and metal catalyst coated on metal oxide

Development of 10 kW-scale hydrogen generator using chemical hydride

Mesostructured Manganese Oxide/Gold Nanoparticle Composites for Extensive Air Purification

A composite adsorbent comprising an acid salt of an m- or p-aromatic amino acid and an acid. The adsorbent may further contain a transition metal compound. The former removes aldehydes, ammonias and amines simultaneously, and the latter further removes hydrogen sulfide. The composite adsorbent is used in the form of a powder, a solution, or a solid supported on a carrier.

Composite adsorbent and process for producing same

The present invention provides a method of generating hydrogen by hydrolyzing a complex metal hydride in the presence of water and a catalyst, wherein the catalyst includes a noble metal and one of metal oxides, metalloid oxides and carbonaceous materials.

Kazuhiro Fukumoto

Papers

Hydrogen generation using sodium borohydride solution and metal catalyst coated on metal oxide

Development of 10 kW-scale hydrogen generator using chemical hydride

Mesostructured Manganese Oxide/Gold Nanoparticle Composites for Extensive Air Purification

Composite adsorbent and process for producing same

Hydrogen generating method and hydrogen generating apparatus