Pt Nanoparticles Supported By Hydrophilic Nitrogen-Doped Porous Carbon for Cathode Catalyst of Micro Direct Methanol Fuel Cell
Authors: Zhang Yujun , Zhang Yufeng , Hou Chenjun , Zhang Xuelin , Liu Xiaowei 
Published: February 2020

Micro direct methanol fuel cell (μDMFC) is effective, safe, environmentally friendly, and is considered as one of the new power sources that will be widely used in portable electronic devices in the future. However, before the fuel cell is put into production, there are still many technical problems that need to be solved. The water management of the cathode is one of the key technical problems. High concentration of methanol feed can only be achieved by reducing water penetration. Nitrogen-doped porous carbon has good water absorption characteristics due to its characteristic porous structure and the hydrogen bonding between nitrogen atoms and water molecules. It can be expected to reduce the water penetration of the cathode and alleviate the water shortage of the cathode when using methanol steam feed. Therefore, the use of nitrogen-doped porous carbon which have a good hydrophilic property as a carrier is one of the methods for improving the water management of a vapor-feed μDMFC.

Herein, we report a preparation process of a cathode catalyst catalyzed by Pt with nitrogen-doped porous carbon as a support. First, the preparation of nitrogen-doped porous carbon is carried out. The graphene oxide, water, formaldehyde and resorcinol are mixed and dissolved, heated in an autoclave for 24 hours and cooled to obtain a precursor, then the precursor is carbonized, heated and cooled. At this point, we obtained the desired nitrogen-doped porous carbon support. Next, the preparation of a 40% Pt-loaded cathode catalyst supported on nitrogen-doped porous carbon was carried out using a standard microwave ethylene glycol method. The isopropanol, nitrogen-doped porous carbon, ethylene glycol and H2PtCl6 were sequentially added and mixed uniformly. The pH of the sample was adjusted to 12, nitrogen gas was input for 10 minutes, and the sample was heated to 130 ℃ in a microwave oven and cooled to room temperature. Then, the pH of the sample was adjusted to 3, followed by suction filtration and lyophilization. At this point we completed the preparation of the cathode catalyst.

We used electrochemical testing to analyze the oxygen reduction performance of the cathode catalyst. The test was carried out in a 0.5 mol L-1 H2SO4 electrolyte and a mercury sulphate electrode was used as a reference electrode. 3 mg sample, 0.5 ml of water, 1.6 ml of isopropanol and 29μl of Nafion were dispersed uniformly and applied to a rotating disk electrode (RDE). Oxygen gas was input into the electrolyte for 20 minutes, before performing cyclic voltammetry (CV) and linear sweep voltammetry (LSV) tests under RDE rotating 1600 laps per minute. The following figure shows the LSV image of a cathode catalyst using carbon as a carrier and nitrogen-doped porous carbon as a carrier, both of which have a Pt loading of 40%. It can be seen that the half-wave potential of the cathode catalyst using carbon as a carrier is 0.81 V, and the half-wave potential of a cathode catalyst supported by nitrogen-doped porous carbon is 0.85 V, which is increased by about 40 mV. It can be seen that the oxygen reduction performance of the cathode catalyst with nitrogen-doped porous carbon as a supporter is improved. Besides, it can be concluded that the as-prepared cathode catalyst will also have good hydrophilic properties, and by using it to fabricate a vapor-feed μDMFC, the water in the cathode can be well preserved to improve the water-shortage problem.

Figure 1