Electrocatalysts for low temperature fuel cells

Catalytic Properties of Biochar as Support Material Potential for Direct Methanol Fuel Cell: A Review

With the evolution and emergence of compounding environmental problems and issues, renewable energy promises to be a sustainable future technology. One technology considered is the fuel cell, which thrives on the primary function of electrocatalytic activities. Thus this review article envisages and presents a comprehensive summary of the applications of activated carbonaceous material as supports for electrocatalysts in fuel cells. The different techniques utilized to produce these carbon materials are discussed in detail. The overview architecture and the principle of the operation of fuel cells are also addressed. Additionally, electrocatalysts and the importance of support materials, their characteristics, and the role they play in the performance of the electrocatalyst will be reviewed. Unfortunately, the carbon-support-based electrocatalyst suffers long-term instability due to corrosion. Previously, carbon black has been used as a carbon support in various fuel cells. In recent years, there has been progress in the incorporation of nanostructured carbon supports in electrocatalysts in various fuel cells; however, there is still a great deal of distance to cover for nanostructured carbon-supported electrocatalysts in fuel cells to realize full commercialization and large-scale industrial purposes due to shortcomings in electrocatalysts, which are low-cost and highly efficient. This review therefore discusses the progress of incorporation of biochar extracted from sugar cane bagasse as carbon support in electrocatalysts for direct methanol fuel cells with the intention to provide insight into the quest of producing highly efficient and low cost fuel cells.

Graphene and Graphene-Like Materials for Hydrogen Energy

The review is devoted to current and promising areas of application of graphene and materials based on it for generating environmentally friendly hydrogen energy. Analysis of the results of theoretical and experimental studies of hydrogen accumulation in graphene materials confirms the possibility of creating on their basis systems for reversible hydrogen storage, which combine high capacity, stability, and the possibility of rapid hydrogen evolution under conditions acceptable for practical use. Recent advances in the development of chemically and heat-resistant graphene-based membrane materials make it possible to create new gas separation membranes that provide high permeability and selectivity and are promising for hydrogen purification in processes of its production from natural gas. The characteristics of polymer membranes that are currently used in industry for the most part can be significantly improved with small additions of graphene materials. The use of graphene-like materials as a support of nanoparticles or as functional additives in the composition of the electrocatalytic layer in polymer electrolyte membrane fuel cells makes it possible to improve their characteristics and to increase the activity and stability of the electrocatalyst in the reaction of oxygen evolution.

Optimization of the Catalytic Layer for Alkaline Fuel Cells Based on Fumatech Membranes and Ionomer

Polymer electrolyte fuel cells with alkaline anion exchange membranes (AAEMs) have gained increasing attention because of the faster reaction kinetics associated with the alkaline environment compared to acidic media. While the development of anion exchange polymer membranes is increasing, the catalytic layer structure and composition of electrodes is of paramount importance to maximize fuel cell performance. In this work, we examine the preparation procedures for electrodes by catalyst-coated substrate to be used with a well-known commercial AAEM, Fumasep® FAA-3, and a commercial ionomer of the same nature (Fumion), both from Fumatech GmbH. The anion exchange procedure, the ionomer concentration in the catalytic layer and also the effect of membrane thickness, are investigated as they are very relevant parameters conditioning the cell behavior. The best power density was achieved upon ion exchange of the ionomer by submerging the electrodes in KCl (isopropyl alcohol/water solution) for at least one hour, two exchange steps, followed by treatment in KOH for 30 min. The optimum ionomer (Fumion) concentration was found to be close to 50 wt%, with a relatively narrow interval of functioning ionomer percentages. These results provide a practical guide for electrode preparation in AAEM-based fuel cell research.

Effect of Metal Composition and Carbon Support on the Durability of the Reversal-Tolerant Anode with IrRu Alloy Catalyst

In polymer electrolyte membrane fuel cells (PEMFCs) for fuel cell electric vehicles, cell reversal (CR) at the anode side can occasionally occur—usually when hydrogen supply is interrupted—which results in degradation of the anode. To mitigate this problem, reversal-tolerant anodes (RTAs) using oxygen evolution reaction catalysts have been generally applied. Adding such materials promotes water oxidation and, thus, provides the protons and electrons during CR situation, while minimizing the carbon-oxidation reaction. In this study, we performed a detailed investigation of the sole use of IrxRuy/C catalysts for RTAs in the membrane electrode assembly (MEA)—including the effects of the IrRu alloy composition and the degree of graphitization of the carbon support on the durability under fuel starvation. Supported IrRu alloy catalysts with different Ir/Ru ratios were prepared via a facile impregnation method on carbon supports with differing degrees of graphitization by heat-treatment at a range of high temperatures. X-ray diffraction patterns indicated that the crystal structure of the alloy nanoparticles depended on the alloy composition, showing the development of a hexagonal closely packed structure with increasing Ru content. Raman spectroscopy indicated an increase in the degree of graphitization of carbon with progressively higher processing temperatures. IrxRuy alloys were found to be a suitable replacement for Pt anode from single-cell MEA performance testing. Furthermore, we examined the synergic enhancement of the CR durability of IrRu alloys with different compositions comparing to the Ir and Ru metals by measuring the initial and total voltage change of MEAs under hydrogen starvation. For the same alloy composition, higher CR durability was observed for MEAs with catalysts prepared using a higher degree of graphitization of the carbon support. Based on the results, we concluded that to develop efficient catalysts for RTAs of automotive PEMFCs, it is important to consider both the durability of the carbon support under high voltages and the catalyst composition.