Growth and detachment of chemical reaction-generated micro-bubbles on micro-textured catalyst

Abstract

This work investigates the growth and detachment of chemically formed micro-bubbles on micro-textured catalyst using a high-speed digital camera and simulation results. Three bubble growth stages were identified for single bubbles grown on circular type Pt catalyst. The first stage was inertia-controlled and the bubble diameter was directly proportional to time, and pertained when the bubble size was smaller than the Pt catalyst; in the second and third stages, gas was generated at a constant rate and the bubble diameter was varied as the cube root of time. However, in the third stage, the bubble growth rate is slightly lower than in the second stage, suggesting saturation. The calculation based on a mathematical model at constant gas generation rate is highly consistent with experimental results. The basic single bubble growth phenomenon was then adopted as a comparison to the bubble growth phenomena on textured catalyst structures. Experimental results revealed that a discontinuous mesh catalyst can effectively shorten the bubble detachment time when the substructures are thoroughly separated and the bubbles are larger than their initial size (~5 μm), while the concentric circular pattern does not. This study provides an insight into the growth and detachment phenomena of chemically formed micro-bubbles on catalyst of different textures, which is useful to the design of reactors for fuel cell systems.