International Journal of Hydrogen Energy 

Abstract: Hydrogen is an ideal energy carrier which is considered for future transport, such as automotive applications. In this context storage of hydrogen is one of the key challenges in developing hydrogen economy. The relatively advanced storage methods such as high-pressure gas or liquid cannot fulfill future storage goals. Chemical or physically combined storage of hydrogen in other materials has potential advantages over other storage methods. Intensive research has been done on metal hydrides recently for improvement of hydrogenation properties. The present review reports recent developments of metal hydrides on properties including hydrogen-storage capacity, kinetics, cyclic behavior, toxicity, pressure and thermal response. A group of Mg-based hydrides stand as promising candidate for competitive hydrogen storage with reversible hydrogen capacity up to 7.6 wt% for on-board applications. Efforts have been devoted to these materials to decrease their desorption temperature, enhance the kinetics and cycle life. The kinetics has been improved by adding an appropriate catalyst into the system and as well as by ball-milling that introduces defects with improved surface properties. The studies reported promising results, such as improved kinetics and lower decomposition temperatures, however, the state-of-the-art materials are still far from meeting the aimed target for their transport applications. Therefore, further research work is needed to achieve the goal by improving development on hydrogenation, thermal and cyclic behavior of metal hydrides.

Abstract: Hydrogen is often considered the best means by which to store energy coming from renewable and intermittent power sources. With the growing capacity of localized renewable energy sources surpassing the gigawatt range, a storage system of equal magnitude is required. PEM electrolysis provides a sustainable solution for the production of hydrogen, and is well suited to couple with energy sources such as wind and solar. However, due to low demand in electrolytic hydrogen in the last century, little research has been done on PEM electrolysis with many challenges still unexplored. The ever increasing desire for green energy has rekindled the interest on PEM electrolysis, thus the compilation and recovery of past research and developments is important and necessary. In this review, PEM water electrolysis is comprehensively highlighted and discussed. The challenges new and old related to electrocatalysts, solid electrolyte, current collectors, separator plates and modeling efforts will also be addressed. The main message is to clearly set the state-of-the-art for the PEM electrolysis technology, be insightful of the research that is already done and the challenges that still exist. This information will provide several future research directions and a road map in order to aid scientists in establishing PEM electrolysis as a commercially viable hydrogen production solution.

Abstract: Hydrogen is the fuel of the future mainly due to its high conversion efficiency, recyclability and nonpolluting nature. Biological hydrogen production processes are found to be more environment friendly and less energy intensive as compared to thermochemical and electrochemical processes. They are mostly controlled by either photosynthetic or fermentative organisms. Till today, more emphasis has been given on the former processes. Nitrogenase and hydrogenase play very important role. Genetic manipulation of cyanobacteria (hydrogenase negative gene) improves the hydrogen generation. The paper presents a survey of biological hydrogen production processes. The microorganisms and biochemical pathways involved in hydrogen generation processes are presented in some detail. Several developmental works are discussed. Immobilized system is found suitable for the continuous hydrogen production. About 28% of energy can be recovered in the form of hydrogen using sucrose as substrate. Fermentative hydrogen production processes have some edge over the other biological processes.

Abstract: Proton-exchange membrane fuel cells (PEMFCs) are considered to be a promising technology for clean and efficient power generation in the twenty-first century. Proton exchange membranes (PEMs) are the key components in fuel cell system. The researchers have focused to reach the proton exchange membrane with high proton conductivity, low electronic conductivity, low permeability to fuel, low electroosmotic drag coefficient, good chemical/thermal stability, good mechanical properties and low cost. These are classified into the “iron triangle” of performance, durability, and cost. Current PEMFC technology is based on expensive perflourinated proton-exchange membranes (PEMs) that operate effectively only under fully hydrated conditions. There is considerable application-driven interest in lowering the membrane cost and extending the operating window of PEMs. PEMFC system complexity could be reduced by the development of ‘water-free’ electrolytes that do not require hydration. It also enables the PEMFC to be operated under ‘warm’ conditions (i.e. above 100 °C) thus further improving its efficiency. Capital cost could also be further reduced because at warmer conditions less Pt could be used. This paper presents an overview of the key requirements for the proton exchange membranes (PEM) used in fuel cell applications, along with a description of the membrane materials currently being used and their ability to meet these requirements. A number of possible alternative candidates are reviewed and presented in this paper. Also discussed are some of the new materials, technologies, and research directions being pursued to try to meet the demanding performance and durability needs of the PEM fuel cell industry. The alternative PEMs are classified into three categories: (1) modified Nafion® composite membranes; (2) functionalized non-fluorinated membranes and composite membranes therein; and (3) acid–base composite membranes. Several commonly used inorganic additives are reviewed in the context of composite membranes. Finally, the general methods of the measuring and evaluating of proton exchange membrane properties have been investigated such as proton conductivity, ion exchange capacity, water uptake, gas permeability, methanol permeability, durability, thermal stability and fuel cell performance test.

Abstract: Hydrogen may be produced by a number of processes, including electrolysis of water, thermocatalytic reformation of hydrogen-rich organic compounds, and biological processes. Currently, hydrogen is produced, almost exclusively, by electrolysis of water or by steam reformation of methane. Biological production of hydrogen (Biohydrogen) technologies provide a wide range of approaches to generate hydrogen, including direct biophotolysis, indirect biophotolysis, photo-fermentations, and dark-fermentation. The practical application of these technologies to every day energy problems, however, is unclear. In this paper, hydrogen production rates of various biohydrogen systems are compared by first standardizing the units of hydrogen production and then by calculating the size of biohydrogen systems that would be required to power proton exchange membrane (PEM) fuel cells of various sizes.