The Autohumidification Polymer Electrolyte Membrane Fuel Cell

A PEM fuel cell was specially constructed to determine kinetics under conditions of welldefined gas phase composition and cell temperature. Steady state multiplicity was discovered in the autohumidification PEM fuel cell, resulting from a balance between water production and water removal. Ignition was observed in the PEM fuel cell for a critical water activity of ~0.1. Ignition is a consequence of the exponential increase of proton conductivity with water activity, which creates an autocatalytic feedback between the water production and the proton conduction. The steady state current in the ignited state decreases with increasing temperature between 50-105°C. At temperatures of >70°C five steady states were observed in the PEM fuel cell. The steady state performance has been followed with variable load resistance and hysteresis loops have been mapped. The dynamics of transitions between steady states are slow ~103 – 104 s. These slow dynamics are suggested to result from a coupling of mechanical and chemical properties of the membrane electrode assembly due to swelling of the membrane with water absorption

Semiconductor–Liquid Junction: From Fundamentals to Solar Fuel Generating Structures

Historically, the investigation of the solid–liquid interface has seen four major breakthroughs: van Troostwijk and Deiman reported the first splitting of water in 1789 using a spark discharge source [1]. Becquerel observed the photoelectric effect at the solid–liquid interface in 1839 [2] and, 183 years after the first water splitting, Fujishima and Honda reported the light-induced dissociation of water at a TiO2 rutile electrode [3]. Three years later, Gerischer published an article demonstrating that a rectifying contact can be realized at the semiconductor–redox electrolyte junction upon judicious choice of the semiconductor–electrolyte pairing [4]. This latter work laid the basis for all present energy-converting electrochemical devices for the conversion of sunlight into electricity or fuels at the solid–liquid interface [5]. Numerous reports followed after this inception of photoelectrochemical energy conversion [6–16] which included the development of regenerative photoelectrochemical solar cells [17–21], water splitting half-cells [22, 23], excitonic solar cells [24], and the dye sensitization cell of Graetzel [25, 26] which represents the first photoelectrochemical solar cell that has been realized as a technical device