Fuel Cells

Abstract

IntroductionFuel cells directly convert chemical energy into electrical energy, without the intermediate formation of heat and mechanical energy as in conventional energy conversion devices based on the Carnot cycle. The direct electrochemical energy conversions of H 2 at the anode and O 2 at the cathode occur spatially separated on two electrodes connected by electrolyte and, in principle, allow for higher energy conversion efficiencies as shown in Fig. 1. The largest efficiency differences between Carnotbased and fuel cell-based energy conversion are found in the low power range of <1 MW and especially <100 kW. These efficiency advantages minimize fuel consumption; furthermore, other environmental concerns are alleviated by fuel cells:• zero or ultra-low emission of pollutants and particulates • reduced noise emissions (some moving parts are part of the balance of plant).Despite these conceptual advantages of fuel cells and their long development history since Grove's discovery in 1893 [1], no real fuel cell markets exist as of today. The reason for this is their still high costs, caused mainly by the required materials and their relatively short lifetime in relation to competitive technologies. Their future market introduction is expected at first for portable applications, followed by stationary applications and finally for transportation applications. This expectation is based on the strong commitment of the car industry, the development of better and cheaper materials and the use of modeling methods to improve fuel cell and fuel cell system efficiencies.Among the different fuel cell types, the low-temperature proton exchange membrane fuel cell (PEMFC), the direct methanol fuel cell (DMFC), the high-temperature molten carbonate fuel cell (MCFC) and the solid oxide fuel cell (SOFC) play the most important roles; historically, the phosphoric acid fuel cell (PAFC) and alkaline fuel cell (AFC) had significant importance. Caused by the low operating temperature of PEMFCs and DMFCs, electrocatalysis-related issues are more critical than in the case of high-temperature fuel cells. Therefore, although this chapter will give a general description of all fuel cell types, it will provide a more in-depth discussion of the anodic oxidation (i.e. for H 2 , CH 3 OH, etc.) * Corresponding author. and cathodic reduction (i.e. O 2 ) reactions occurring in PEMFCs and DMFCs; where appropriate, findings will be compared with the phosphoric acid fuel cell literature. Working Principles of Fuel CellsFuel cells are electrochemical power sources (ECPS), similar to primary and secondary batteries (also referred to as accumulators). Their working principle is shown schematically in Fig. 2. These electrochemical cells consist of two electrodes separated by an ionically conducting electrolyte. Conversion of chemical energy into electrical energy occurs at the interface between the electronically conducting electrodes and the ionically conducting electrolyte. In principal, the electrodes can operate in two modes, either transforming elec...

Scalable Synthesis of Carbon-Supported Platinum–Lanthanide and −Rare-Earth Alloys for Oxygen Reduction

“…Proton exchange membrane fuel cells (PEMFCs) are among the most promising renewable energy technologies, capable of producing electricity through electrochemical reactions of hydrogen and oxygen fuels at near room temperature (<80 °C) operating conditions. − However, the high platinum loading at the cathode side strongly limits the expansion of hydrogen vehicles on the market . Over the years, the loading at the anode could be reduced to 0.05 mg cm –2 .…”

Electrocatalytic Measurement Methodology of Oxide Catalysts Using a Thin-Film Rotating Disk Electrode

“…5 The measured ORR currents were then corrected for O 2 mass transport resistances using the Levich equation to obtain the ORR activity of the catalyst. Compared with ORR activity measurements in fuel cells, which require time-consuming optimization of membrane electrode assemblies ͑MEAs͒ for each catalyst, the thin-film RDE method is a fast screening tool to obtain ORR activities, which are consistent with those obtained in MEAs, 8 and it has led to the discovery of highly active novel ORR catalysts. [9][10][11] While noble metal catalysts with significantly enhanced activity compared with conventionally used Pt/C may enable commercialization of PEMFCs, AMFCs and metal/air batteries offer an alternative route toward low cost, noble-metal-free fuel cells.…”

Understanding the electrocatalysis of oxygen reduction on platinum and its alloys

“…7,[23][24][25][26][27][28][29][30] This is achieved by forming a structure with a Pt overlayer on a core with a different composition. Typically, the core consists of Pt alloyed with a less noble late transition 3d metal such as Fe, Co, Ni, and Cu, although it might contain other Jan Rossmeisl Since 2009 Jan Rossmeisl has been an Associate Professor at the Department of Physics at DTU.…”