Fabrication Of Pt/Co₃O₄NWs/TiO₂NTs Electrode And Its Electrocatalytic Performance For Direct Methanol Full Cells

This paper introduces the structure, working principle, research progress and themain existing problems of the direct methanol fuel cells (DMFC), and conducts acomprehensive review about the research status of anode catalyst for DMFC.Meanwhile, the preparation and application of cobalt oxide (Co3O4) materials werereviewed. Novel Pt/Co3O4NWs/TiO2NTs composite electrode was successfullyfabricated by the combination of the improved ammonia-evaporation induction methodfor Co3O4nanowires growth on TiO2NTs substrates and the electro-deposition for Ptloading on Co3O4NWs/TiO2NTs. The obtained electrodes were employed as catalyst formethanol oxidation in alkaline media. The crystal morphology and electrochemicalperformance of these electrodes was detected by XRD, SEM, EDS, XPS and CHI660D.The main contents are as follows:Co3O4NWs/TiO2NTs electrode was successfully achieved by the improvedammonia-evaporation induction method, and the growth mechanism of Co3O4NWs wasdiscussed initially in this paper. The influence on the Co3O4NWs microstructure by thedifferent cobalt salt concentration in the precursor solution was studied. It is found thatCo3O4NWs obtained by0.1mol/L Co(NO3)2in the original solution has the bestmicrostructure with an average diameter of ca.600nm and lengths up to ca.15-20μm.And the individual nanowire has a fold appearance consisting of ring architectures witha hollow interior. What is more, the inside and outside wall of the hollow is also quiterough and the size of the hollow is about400nm, which makes a great contribution tosignificantly improve the specific surface areas of the nanowires. This Co3O4NWs/TiO2NTs electrode obtained by0.1mol/L Co(NO3)2in the original solution has the bestelectric catalytic activity for the oxidation of methanol and the lowest charge transferresistance (3.74), so this Co3O4NWs/TiO2NTs was used as the substrate of Ptnanoparticles electrodeposition.Pt/Co3O4NWs/TiO2NTs composite electrode was prepared by the electro-deposition for Pt loading on Co3O4NWs/TiO2NTs. In order to study the role ofCo3O4NWs in the electrode, the same method was employed for platinum deposition onbare TiO2NTs, and the electrodes thus obtained were also used for comparison. TheEDS figure shows that the Pt/Co3O4NWs/TiO2NTs composite electrode has the mainelements of Ti, O, Co and Pt. The results also show that the introduction of Co3O4NWs will ensure better electrical conductibility, more efficient use of the noble metal andbetter toleration to CO poisoning during methanol oxidation which may be related withthe much higher surface concentration of stable oxygenated species of platinumobserved from Pt/Co3O4NWs/TiO2NTs.Cyclic voltammetry and chronoamperometry were taken on Pt/Co3O4NWs/TiO2NTs and Pt/TiO2NTs electrodes for methanol oxidation. It shows that Pt/Co3O4NWs/TiO2NTs electrode has more excellent electrocatalytic activity, electrocatalyticstability and better toleration to CO poisoning during methanol oxidation thanPt/TiO2NTs without Co3O4. It is because that Co3O4NWs contains much more OHadswhich can oxidize CO to CO2. And the existence of Co3O4can inhibit CO adsorption onthe surface of the electrode. The Pt oxygen species in Pt/Co3O4NWs/TiO2NTs electrodeplay a role of oxygen donor which can promote CO oxidation. The bifunctionalmechanism is available to explain why the Pt/Co3O4NWs/TiO2NTs electrode has bettercatalytic activity, stability and resistance to CO.