(181b) A New Methodology to Screen Water Splitting Cycles for Hydrogen Production

The use of thermochemical and electrochemical cycles to split water has been object of several studies. Some screeneing attempts have been made by assigning scores to different cycle properties (Brown et al., 2000). More recently, Lewis (2005) analyzed cycles more systematically by using pinch analysis to determine heat requirements. These attempts, however, do not take into account the energy expenditure in separation, nor includes measures to deal with incomplete conversion reactions, like the use of excess reactants. In this paper, we developed a systematic methodology for evaluating and screening water-splitting cycles. To do this, we first define the thermodynamic efficiency of a cycle using the minimum reversible energy (heating and work) requirement. We base this calculation on a new algorithm that uses excess reactants for reactions that are not spontaneous (high negative ÄG) as well as minimum utility calculations using the heat pinch method. We also include the separation work, when needed. We then assess the real efficiency of the cycle by estimating real minimum heating utility as well as separation energy. We finally optimize the cycles for T, P and excess reactants and provide examples.