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.

PROBLEM TO BE SOLVED: To provide a catalyst capable of decomposing and removing ozone efficiently even in an atmosphere of a low ozone concentration and a high humidity.SOLUTION: The catalyst for ozone decomposition and removal includes a support, the first catalyst ingredient consisting of at least one selected from the first metals of Cu, Co and Ni, alloys of the first metals and alloys of at least one of the first metals with other metals and coated on the surface of the support by electroless plating, and the second catalyst ingredient consisting of at least one selected from the second metals of Ag, Pd, Ir, Pt, Rh, Ru, Os and Au, alloys of at least one of the second metals and alloys of the second metals with other metals and supported, by electroless plating, on the surface of the first catalyst ingredient and inside the same.

Catalyst for decomposition and removal of ozone, method of producing the same, and ozone decomposition/removal method using the same

A catalyst for purification of exhaust gases

PROBLEM TO BE SOLVED: To provide a filter for removing sulfur-based gas, which can exhibit satisfactorily high removal performance to sulfur-based gas at present and over a long period of time. SOLUTION: The filter 1 for removing sulfur-based gas, which is brought into contact with the sulfur-based gas in a gas flow passage to remove the sulfur-based gas, is composed of a preceding-stage filter 11 to be arranged on the upstream side of the gas flow passage and a succeeding-stage filter 12 to be arranged on the downstream side of the gas flow passage. The preceding-stage filter 11 is provided with a first sulfur-based gas removing material consisting of a porous carrier and the iodine deposited on the porous carrier. The iodine is produced by catalytically pyrolyzing ammonium iodide at ≥80% pyrolysis rate by using the porous carrier as a catalyst. The succeeding-stage filter 12 is provided with a second sulfur-based gas removing material consisting of an activated carbon fiber and the alkali component deposited on the activated carbon fiber. COPYRIGHT: (C)2009,JPO&INPIT

Filter for removing sulfur-based gas and method for removing sulfur-based gas using the same

PROBLEM TO BE SOLVED: To provide a hydrogen generating apparatus which can keep the generation quantity of hydrogen constant for a long time and which can be miniaturized. SOLUTION: This invention relates to an apparatus for generating hydrogen by feeding water and a complex metal hydride into a vessel 2 which contains a catalyst and hydrolyzing the complex metal hydride in the presence of the catalyst. The apparatus is provided with a vessel 3 for feeding water to the vessel 2, a vessel 4 for feeding the complex metal hydride to the vessel 2, a water recovering device for recovering water from an aqueous solution in the vessel 2 and a returning means L8 for returning water recovered by the water recovering device to the vessel 3. When water and the complex metal hydride are fed into the vessel 2 from the vessels 3 and 4, respectively, the complex metal hydride is hydrolyzed in the presence of the catalyst to generate hydrogen. Water is recovered from the aqueous solution in the vessel 2 by the water- recovering device and returned to the vessel 3 by the returning means L8.

Hydrogen generating apparatus

PROBLEM TO BE SOLVED: To provide a hydrogen generating catalyst which is capable as well of attaining enough hydrogen generating rate and quantity as of being repeatedly usable and easily controlled in its hydrogen generating quantity, when a soluble metal hydride is hydrolyzed to generate hydrogen, and a method and an apparatus for generating hydrogen using it. SOLUTION: The hydrogen generating catalyst is characterized by being composed of a noble metal and a composite metal oxide containing Li.

Kazuhiro Fukumoto

Papers

Catalyst for decomposition and removal of ozone, method of producing the same, and ozone decomposition/removal method using the same

A catalyst for purification of exhaust gases

Filter for removing sulfur-based gas and method for removing sulfur-based gas using the same

Hydrogen generating apparatus

Hydrogen generating catalyst, method and apparatus for generating hydrogen using it