(181c) An Algorithm for Systematic Generation of Thermochemical Cycles for Water Splitting

Thermochemical cycles for water splitting are attractive for the production of hydrogen for fuel cell applications and are, hence, receiving serious consideration. However, the selection of feasible cycles from among the enormous number of possibilities is an onerous task that is currently done manually on an ad hoc basis. We have developed an algorithm that performs this task in a systematic and exhaustive manner. Thus, based on the observation that a thermochemical cycle is tantamount to a reaction route, we employ the previously developed concept of minimality in defining response reactions (RERs) and direct reaction routes (RRs) to develop an algorithm for a systematic enumeration of thermodynamically feasible thermochemical cycles for water splitting. The input is a set of chemical species along with their thermodynamic characteristics. A unique set of reactions is next generated from this list using the stoichiometric formalism of RERs. These are further screened and reduced to a subset of thermodynamically favorable RERs. Alternatively, the reactions may be selected from a separately build database of chemical reactions. The reactions are next assembled into direct RRs (thermochemical cycles), i.e., linear combinations of reactions that produce the desired overall reaction (OR), namely, 2H2O = 2H2 + O2. Only the direct RRs that satisfy the thermodynamic feasibility condition are further retained. The proposed algorithm is a new powerful tool for automatic generation and screening of thermodynamically feasible thermochemical cycles.