Abstract
This research mainly focus on the observation of micro-bubble and electrocatalytic test of anode for micro direct methanol fuel cells (μDMFC). We can discuss this issue from two parts. The first part is observing the CO2 micro-bubble and measure electrochemical signal simultaneously on different catalyst substrate electrodes. The second part is using CCD camera and high speed camera to observe the O2 micro-bubble growth and detached phenomenon on different type patterns of the diameter 80 μm Pt film. We can concluded from part one that using carbon nano tube (CNTs) as catalytic support can get less bubble accumulation on electrode surface and lead to improvement of the CO2 microbubble detaching capability. Also, the high bubble detachment rate and smaller detachment size observed in the optical system are consistent with the high frequency of current vibration in the electrochemical system. These results demonstrate that electrodes with nanostructures contribute to the mass transfer for electro-catalytic reactions composed of liquid reactants and gaseous products. The uncovered reaction area on the Pt/CNT/CC electrode was 34%, and was 32% higher than that on the Pt/CC and Pt/CP electrodes, respectively, which equates to a 34% and 32% performance enhancement, respectively, in the CNT-modified electrodes (Pt/CNT/CC) due to a faster CO2 bubble removal capability. At the second part of micro-bubble observation, we investigate the growth and detachment of chemically formed O2 micro-bubbles on micro-textured catalyst using a high-speed digital camera and simulation results. Three stages of bubble growth on a solid circular Pt catalyst were determined experimentally to be as follows. The first stage is one of inertial control (time <0.2s); the second stage is one of constant gas generation rate and increasing footing area (0.2< time <2.5s), and the third stage is one of constant gas generation rate with constant footing area (time >2.5s). These results are highly consistent with theoretical predictions based on footing area visualization. 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 um), while the concentric circular pattern does not. The footing area of the mesh catalyst is suggested to be smaller than that of the solid circular and concentric circular catalyst, promoting the generation of gas and simultaneously reducing the adhesive force between bubble and catalyst. These findings will be beneficial for the design of an anode chamber in μ DMFC in the future.