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Solid: Protons

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Introduction: It may seem something of a truism to describe an element as unique, but hydrogen is certainly one of the more unusual elements in the periodic table. It is the lightest element and consists of only a proton and an electron and is thus the only element not to contain a neutron in its main isotope (1H). In its stable molecular form (H2), it is also the least dense and the most abundant in the universe. Perhaps surprisingly, given that its low density results in gaseous hydrogen being almost nonexistent in the Earth’s lower atmosphere, it is also the. | Solid Protons J Tolchard Norwegian University of Science and Technology Trondheim Norway 2009 Elsevier B.V. All rights reserved. Introduction It may seem something of a truism to describe an element as unique but hydrogen is certainly one of the more unusual elements in the periodic table. It is the lightest element and consists of only a proton and an electron and is thus the only element not to contain a neutron in its main isotope 1H . In its stable molecular form H2 it is also the least dense and the most abundant in the universe. Perhaps surprisingly given that its low density results in gaseous hydrogen being almost nonexistent in the Earth s lower atmosphere it is also the third most abundant element on the Earth s surface. The key to this of course lies in its chemistry and this is where its uniqueness is truly apparent In compounds hydrogen shows remarkable flexibility in its ability to bond to both covalent and ionic systems. It also demonstrates a unique bonding capability in the form of the hydrogen bond which although weak is crucial in properties as seemingly unrelated as the boiling point of water the structure of DNA and of course the focus of this work proton conductivity. So why are proton-conducting electrolytes so interesting Basically it comes down to the reaction 1 H 2O2-H2O I This simple reaction releases a significant quantity of energy DGf 237 kJ mol 1 at 25 C with the only by-product being pure water. Hydrogen is thus an extremely attractive replacement to the hydrocarbon fuels widely used today. However to achieve this replacement a means to both generate large quantities of H2 and utilize it in a safe and efficient manner is required. There are several ways to achieve both these goals but probably the most promising and the most efficient in terms of utilization is electrochemical conversion. Electrochemical conversion processes offer the ability to directly convert the energy released in reaction I to electricity thus avoiding the .