Abstract
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•New mechanism for methanol oxidation over Ni-based catalysts is introduced.•Methanol electooxidation occurs into two successive mechanisms.•Pre-activation of the Ni-based electrocatalysts is not a mandatory step.•The study terminates the doubt about utilizing Ni-based electrodes in the fuel cells.
The study proved that synthesis of the Ni(OOH) active layer over nickel-based electrocatalysts before utilization in methanol electrooxidation is not an important step and the oxidation process can start over the inactivated surface. Based on XPS analysis and the electrochemical measurements, the electrooxidation process can take place over the bared nickel surface by means of the predominant Ni(OH)2 thin layer with formation of the Ni(OOH) as by product; the reactions were explained by a newly proposed mechanism. Later on, due to abundance of the conventional active layer, the oxidation process returns to the ordinary mechanism until exhaustion of the NiOOH layer then the oxidation reactions return back to be Ni(OH)2-dependent and so forth. Accordingly, it was discovered that the methanol oxidation process can be done continuously on the surface of the inactivated Ni-based materials by two successive mechanisms. Ni-decorated graphene was synthesized and exploited as an effective Ni-based electrocatalyst, the catalyst model was characterized by XRD, TEM and Raman spectroscopy analyses. Overall, the study introduces a novel characteristic for the nickel-based electrocatalysts and opens a new avenue for those cheap electrode materials to be exploited in the fuel cells.