(83j) Controlled Hydrogen Peroxide Decomposition for a Solid Oxide Fuel Cell (SOFC) Oxidant Source with Microreactors

It is well established that the catalytic decomposition of hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2) [H2O2 → H2O + ½ O2] is highly exothermic (Heat of Reaction: 98 kJ/mol) and notoriously susceptible to thermal runaway. However, liquid hydrogen peroxide has high oxygen density making it a particularly attractive oxidant for undersea naval power applications where air-independence and space limitations elicit additional power supply design challenges. Microchemical technologies have inherently higher surface-to-volume ratios which facilitate heat and mass transfer. Small-scale geometry thus offers a mechanism to harness the benefits of hydrogen peroxide decomposition as an oxidant source while reducing the risk of uncontrollable heat rise.

This study investigated two small-scale reactors to illustrate thermal management and oxygen production feasibility during the multiphase decomposition of hydrogen peroxide as an oxidant for an unmanned undersea vehicle (UUV) solid oxide fuel cell (SOFC). A microscale packed bed (MPB) reactor model and miniature tubular, catalyst-coated (TCC) reactor model were developed in the finite element modeling program COMSOL. The properties of the multiphase product stream were described by weighted averages of the components in the stream. This approach assumed that the reactant stream maintained a well-mixed, dispersed phase. The heat generated during simulated decomposition in the convectively cooled reactor channels caused temperature rises greater than 400 K (neglecting the energy required to evaporate water). With small-scale geometry alone unable to prevent significant heat rise, further cooling was needed to ensure thermal management of the reactor zone. The addition of extended surface areas, improved passive cooling of the reactor units and simulated temperature rises decreased to less than 20 K under the previous reaction conditions.

Experimental data collected with a physical TCC reactor demonstrated increased variability in both the temperature and oxygen production data at higher hydrogen peroxide concentrations. The increased production of oxygen gas from higher hydrogen peroxide concentrations resulted in long pockets of oxygen gas within the physical reactor that periodically prevented reactant decomposition. Since the models averaged the instantaneous properties of the products into a single effluent fluid, the physical effect on decomposition due to separated oxygen gas was not evident during simulation. Despite the occurrence of slug flow instead of dispersed flow, both sets of results showed that sufficient oxygen generation and thermal control during hydrogen peroxide decomposition is feasible provided the reactor subunits have sufficient surface area-to-volume ratio to facilitate convective cooling.