Bad Direct Formic Acid Fuel Cell Anode Pd Catalyst Electrocatalytic Stability Mechanism Analysis And Improvement Methods

Recently, direct formic acid fuel cell (DFAFC) has attracted considerable attention due to its many advantages. However, DFAFC has two major shortcomings that limit its lifespan and performance:(i) the poor electrocatalytic stability of the carbon supported Pd (Pd/C) catalyst and (ii) rapid decomposition of formic acid over the Pd/C catalyst. In this thesis, two major shortcomings are combined to investigate. The following four methods are used to improve the electrocatalytic stability of the Pd/C catalyst and inhibit the decomposition of formic acid over the Pd/C catalyst:1. improvement of electrocatalytic performance of carbon supported Pd anodic catalyst in direct formic acid fuel cell by ethylenediamine-tetramethylene phosphonic acidThe Pd/C catalyst is modified with ethylenediamine-tetramethylene phosphonic acid (EDTMP) at the room temperature. The resulting catalyst is designated as Pd/C-E catalyst. We found that the Pd/C-E catalyst possessed improved electrocatalytic activity and stability for formic acid oxidation. The excellent electrocatalytic performance of the Pd/C-E catalyst may be attributed to inhibiting the decomposition of formic acid and to promoting the oxidation of formic acid through the direct pathway.2. New insights into enhanced electrocatalytic performance of carbon supported Pd-Cu catalyst for formic acid oxidationThe Pd-Cu/C catalysts with different atomic ratios of Pd and Cu and high alloying degree are successfully synthesized with a simple impregnation-reduction method. It is noticed that the atomic ratio of Pd and Cu has a significant effect on the electrocatalytic performances of the Pd-Cu/C catalysts and the decomposition rate of formic acid over the Pd-Cu/C catalysts. As the decomposition rate of formic acid over the Pd/C, Pd7Cu1/C, Pd5Cu1/C and Pd3Cu1/C catalysts is decreased gradually, the electrocatalytic activity and stability of these catalysts for formic acid oxidation are increased accordingly. This is ascribed to that the decrement of the decomposition rate of formic acid over the Pd-Cu/C catalysts decreases the CO production, which would decrease the poison of the Pd-Cu/C catalyst. Although the Pd1Cu1/C catalyst can also inhibit the decomposition of formic acid completely, the lower electrocatalytic performance of the Pd1Cu1/C catalyst is due to more Cu atoms existing on the surface and a larger amount of PdO and CuO compared to the Pd3Cu1/C catalyst. Taken together, the Pd3Cu1/C catalyst shows the best electrocatalytic activity and stability for formic acid oxidation and has potential application in DFAFC.3. Promoting effect of silicotungstic acid on carbon supported Pd anodic catalyst for direct formic acid fuel cell applicationThe Pd/C catalyst is modified with silicotungstic acid (SiWA) at80℃from the water bath. It is found that the resulting Pd/C-SiWA catalyst displayed the improved electrocatalytic activity and stability for formic acid oxidation, as compared to the Pd/C catalyst. This is attributed to that the Pd/C-SiWA catalyst not only possesses a much higher tolerance toward COads poisoning but also inhibits the decomposition of formic acid.4. Enhanced electrocatalytic performance of carbon and phosphotungstic acid supported Pd anodic catalyst for formic acid oxidationThe Vulcan XC-72R carbon is modified with phosphotungstic acid (PWA) at80℃from the water bath. The resulting hybrid support is designated as PWA/C. The resultant Pd-PWA/C catalyst was prepared by using a simple impregnation-reduction method to load Pd on PWA/C hybrid support. It is found that the electrocatalytic activity and stability of the Pd-PWA/C catalyst for formic acid oxidation are much better than that of the Pd/C catalyst. It is due to the strong interaction between Pd and PWA/C, leading that the Pd-PWA/C catalyst not only possesses a much higher tolerance toward COads poisoning but also inhibits the decomposition of formic acid.