Insight Into The Reaction Mechanisms Of Methanol Dehydrogenation And Oxidation On PtRu And PdCu

As a new energy,Direct methanol fuel cells?DMFCs?can alleviate environmental pollution,energy shortage and other issues.At present,the main problems of DMFCs are the low catalytic activity of the catalyst and CO poisoning.The study found that Pt alloy and Pd alloy have higher catalytic efficiency for the direct methanol fuel cells,and they can improve tolerance toward CO poisoning.Periodic DFT calculations have been performed to systematically investigate the mechanisms of methanol decomposition and oxidation on the PtRu/Pt?111?and PdCu?111?surfaces.Geometries and energies for the primary species involved were analyzed and the reaction network were mapped out.The most favorable pathway for methanol decomposition on PtRu/Pt?111?surface is the initial O�H bond scission,whose energy barrier is lower than the initial C�H bond scission and initial C�O bond scission.The decomposition of CH₃OH occurs via the path CH₃OH?CH₃O?CH₂O?CHO?CO with the limiting step of the second dehydrogenation.For the oxidation reaction of methanol on PtRu/Pt?111?surface,although the oxidation of CO is hindered by a high barrier,the CHO oxidation to HCOOH could occur facilely.Further decomposition of formic acid to CO₂ and/or CO could occur via four possible pathways,that is,initial C-H,O-H,and C-O bond activations as well as simultaneous activation of C-H and C-O bonds,where the first pathway,HCOOH?COOH?CO₂,is the most favorable from a kinetic point of view.Our calculated results indicate that methanol on PtRu/Pt?111?prefers to decomposition rather than desorption and then oxidation via non-CO pathway rather than CO pathway for pure Pt,which indicates that PtRu alloy can improved tolerance toward CO poisoning compared with pure Pt.The most favorable pathway for methanol decomposition on PdCu?111?surface is the initial C�H bond scission,which is different from the Pt Ru/Pt?111?alloy surface.The decomposition of CH₃OH occurs via the path CH₂OH?CH₂OH?CH₂O?CHO?CO with the limiting step of the CH₂OH dehydrogenation.Because the energy barrier of CHO?CO+H is too high to occur,CHO prefers to react with OH to generate HCOOH rather than dehydrogenation.For the further decomposition of HCOOH,HCOOH?COOH?CO₂ is found to be the most favorable pathway from the kinetic and thermodynamic points of view.The most favorable pathway for methanol decomposition and oxidation on PdCu?111?surface is CH₃OH?CH₂OH?CH₂O?CHO?HCOOH?COOH?CO₂,whose limiting step is CH₂OH?CH₂O+H.Furthermore,the CO oxidation to CO₂ could occur facilely,which indicated that CO produced in the reaction process can be easily oxidized to CO₂.It also indicated that PdCu alloy can improved the tolerance toward CO poisoning compared with pure Pd.