Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy

Abstract

The generation of energy by clean, efficient and environmental-friendly means is now one of the major challenges for engineers and scientists. Fuel cells convert chemical energy of a fuel gas directly into electrical work, and are efficient and environmentally clean, since no combustion is required. Moreover, fuel cells have the potential for development to a sufficient size for applications for commercial electricity generation. This paper outlines the acute global population growth and the growing need and use of energy and its consequent environmental impacts. The existing or emerging fuel cells’ technologies are comprehensively discussed in this paper. In particular, attention is given to the design and operation of Solid Oxide Fuel Cells (SOFCs), noting the restrictions based on materials’ requirements and fuel specifications. Moreover, advantages of SOFCs with respect to the other fuel cell technologies are identified. This paper also reviews the limitations and the benefits of SOFCs in relationship with energy, environment and sustainable development. Few potential applications, as long-term potential actions for sustainable development, and the future of such devices are discussed.

Introduction

Today fuel cells are much in the news since they appear to be one of the most efficient and effective solutions to environmental problems that we face today. It is now well established that global warming is taking place due to effluent gas emission, mainly CO₂. During the past century, global surface temperatures have increased at a rate near 0.6°C/century [1]. This trend has dramatically increased during the past 25 years: the temperature rise is 2.3, 1.3 and 1.7°C according to the three well-known centres assessing this phenomenon i.e., Princeton in the USA, Hamburg in Germany, and IPCC of London in the U.K. Moreover, according to the US National Oceanic and Atmospheric Administration and the Scripps Institute of Oceanography in San Francisco, the average temperature of the Atlantic, Pacific and Indian Oceans (covering 72% of the earth’s surface) has risen by 0.06°C since 1995. Global temperatures in 2001 were 0.52°C above the long-term 1880–2000 average (the 1880–2000 annually averaged combined land and ocean temperature is 13.9°C). Also, according to the US Department of Energy (DoE), world emissions of carbon are expected to increase by 54% above 1990 levels by 2015 making the earth likely to warm 1.7–4.9°C over the period 1990–2100, as shown in Fig. 1 [2]. Table 1, Table 2, Table 3 show respectively the total CO₂ emissions of the top 15 nations, the CO₂ emissions of top industrial nations per capita and by unit Gross National Product (GNP) [3].

Problems with energy supply and use are related not only to global warming but also to such environmental concerns as air pollution, acid precipitation, ozone depletion, forest destruction, and emission of radioactive substances.

World population keeps increasing at 1.2–2% per year, so that it is expected to reach 12 billions in 2050. Therefore, economic development will almost certainly continue to grow. Global demand for energy services is expected to increase by as much as an order of magnitude by 2050, while primary-energy demands are expected to increase by 1.5 to 3 times [4], as seen in Table 4. As worldwide oil supplies dwindle (Fig. 2 [5]), the development of new power generation technologies will become increasingly important. Simultaneously, interest will likely increase regarding energy-related environmental concerns. Indeed, energy is one of the main factors that must be considered in discussions of sustainable development. In response to the critical need for a cleaner energy technology, some potential solutions have evolved, including energy conservation through improved energy efficiency, reduction in the consumption of fossil fuels, and an increase in the supply of environmental-friendly energy, such as renewable sources and fuel cells. Electricity from fuel cells can be used in the same way as grid power. One such technology is the solid oxide fuel cell (SOFC), which is one of the most efficient and environmental-friendly technologies available for generating power from hydrogen, natural gas, and other renewable fuels. Large-scale, utility-based SOFC power generation systems have reached pilot-scale demonstration stages in the US, Europe, and in Japan. Small-scale SOFC systems are being developed for military, residential, industrial, and transportation applications.