Facile Synthesis Of Highly Porous NiO Film With Excellent Electrocatalytic Activity Towards Methanol Oxidation

In recent years, various nickel-based materials such as metallic nickel, nickel alloys and nickel compounds are considered to be the promising non-Pt based electrocatalysts in direct methanol fuel cells(DMFC) because of the high electrocatalytic performance, reduced cost and good stability. Many efforts have been devoted to the synthesis of various nanostructured Ni-based materials by different methods. Although significant progress has been achieved, it is still challenging to prepare non-Pt catalyst with both excellent activity and good durability.Anodization is an electrochemical technique to produce nanostructured material. The anodic films can be easily designed to achieve different nanostructure or morphology, and have shown outstanding performance in versatile applications. It is natural to expect that anodization can be extended to nickel for the fabrication of efficient electrocatalyst, which provides a direction to solve the above mentioned problems of Ni-based catalysts. Therefore, the purposes of the study are to prepare highly porous NiO film by a facile and fast anodization and annealing approach. By optimizing anodization and annealing processing parameter, the film can be better applied to the field of DMFC anode catalysts.In this paper, the influences of various anodization conditions such as solution concentration, temperature and processing time were studied in detail firstly to obtain the optimized anodization process(0.5 wt% NH4 F + 85 wt% H3PO4, 20℃ and 5 min). Then a series of annealing treatment are carried out to improve film’s activity and durability. By studying the influence of annealing temperature and time to its performance, the detailed processing parameters(400℃ and 20 min) are attained.The anodic NiO film was fabricated under the optimized condition. The surface morphology, crystalline structure, electrochemical properties and the energy storage mechanism of anodic films were investigated. The as-prepared NiO films were composed of evenly distributed mesopores and nano-crystals less than 10 nm, which not only facilitate electrolyte penetration, but also shorten ions diffusion distance and provide more electro-active sites. Anodic NiO film is grown in-situ on the metallic substrate with strong adhesion strength. Problems such as nanoparticles agglomeration and loss of contact with the current collector are effectively avoided. The anodic NiO film exhibited faster reaction kinetics, better stability and enhanced activity in comparison with many other state-of-the-art Ni-based catalysts. As anodization is a simple, low cost and easily scaled up method, the work described here is promising to speed up the practical application of non-Pt catalyst for DMFC.