Fe-co Based Oxides Nanoarray:Syntheses And Electrocatalytic Performance

Nanostructured arrays is a periodic and ordered structure where the nanounits constructed on one-dimensional, two-dimensional, or three-dimensional on the surface of substrates. This kind of architecture demonstrates remarkable physical and chemical properties in terms of their confined dimensions and the combination of bulk and surface properties, and then expands the scope of the study of new advanced functional materials. Particularly, transition metal oxides nanoarrays are of great interest because of its natural abundance, low cost, stability, tunable band gap, etc.. Therefore, the applications of nanostructure arrays are very broad including catalysis, energy storage and so on. Iron oxide (α-Fe2O3) and cobalt oxide (Co3O4) are two of the most extensively studied oxides in current researches.Here, we reported an easy and facile chemical bath deposition method to obtain α-Fe2O3and MxCo3-xO4nanostructure arrays with precisely controlled morphology, and further investigated their electrocatalytic performances. This study is helpful for people to understand the relationship between the morphology and their properties. In this paper, the main achievements were summarized as follows:1. By optimizing reaction conditions (pH, iron source, temperature and surfactant), α-Fe2O3nanocrystals with different morphologies were obatined (Fe-SC, Fe-LC, Fe-SR, Fe-LR). It is found that, the predominantly exposed planes of α-Fe2O3nanocrystals significantly influenced the catalytic activity of CO oxidation. Fe-LR with more reactive crystal plane{110}, which has a relative higher density of Fe atoms, showed a higher activity than the other samples with less exposed{110}.2. Sea urchin-like Ag-α-Fe2O3composites provided an exciting platform for high and fast gas-sensing. The general fabrication protocol for constructing hierarchical nanostructures included a hydrothermal reaction and a subsequent incipient wetness impregnation process. Based on the shape evolution, we deduce a formation mechanism. The physical properties (large surface area, porous structure) and the combinations of sensitization effect from Ag nanoparticles endow the Ag-α-Fe2O3composites with enhanced gas-sensing properties, for examples, a wide detection range, a lower detection concentration, and a higher sensitivity. In addition, a possible gas-sensing mechanism has been proposed.3. In an effort to obtain a biosensor suitable for high-efficiency biosensing, herein we report on the fabrication and electrocatalytic performances of α-Fe2O3nanorod (NR) arrays. Such electrode obtained by the anodic electrochemical deposition. The NR arrays electrode showed superior biosensing properties for both NO2-and H2O2. A wide linear response range (2×10-7-5×10-3M), high sensitivity (135.36μA mM-1cm-2), and low detection limit (1×107M) were obtained for oxidation of nitrite. As for H2O2reduction, a detection limit of2×10-7M, linearity as5×10-7to3×10-3M and a sensitivity of77.30μA mM-1cm-2could be obtained for this NR arrays electrode. Meanwhile, the stability and interference rejection of the biosensor were also considered.4. We reported the first demonstration of controlled growth of α-Fe2O3arrays with different preferentially exposes facets as a simple and effective strategy to fundamentally improve the photoelectrochemical water splitting. In comparison to [100]-oriented α-Fe2O3nanowalls array (Fe-NWs), porous α-Fe2O3nanopillars array (Fe-NPs) with exposed [110] facets showed a dramatic shift in the onset potential from0.86V to0.68V (vs. RHE) and an increase in the plateau photocurrent from1.20mA cm-2to0.20mA cm-2. Preliminary experiments on incident-photon-to-current-conversion efficiency (IPCE) spectrum of Fe-NPs is calculated to be～15.94%(at360nm), which is superior to the values of4.91%for the Fe-NWs. The Fe-NPs sample showed a red shift in the bandgap transition that confirmed by UV-visible absorption spectra. Porous structure,(110) facet, and oxygen vacancy in NPs significantly improved its adsorption, electronic, and photocatalytic properties, which are responsible for the enhanced electrocatalytic activity for water oxidation.5. Hierarchical ZnxCo3-xO4nanoarrays were fabricated by co-depositing mixed metal (Zn and Co) nitrites in alkaline solution followed by calcination in air, and further we investigated its eletrocatalytic performance for OER. Only a small overpotential of-0.32V with a Tafel slope of51mV/decade could be obatined for the Zn/Co=1/3sample. The superior OER activity of the ZnxCo3-xA:O4nanoarrays could be attributed to optimized chemical environments for Co ions and construction of hierarchical pillar arrays.6. Except for doping with other transition element to enhance the OER activity, loading with noble metal is another promising strategy. In this work, a facile hydrothermal process was demonstrated to successfully fabricate NiCo2O4nanorod arrays, and then followed by a reduction process to obtain Au coupled NiCo2O4. The Au/NiCo2O4electrode was found to be a promising catalyst for OER. When the amount of Au was2.0wt%, the Au/NiCo2O4hybrid electrode showed a higher OER activity than other counterparts. The incorporation of Au could be acted as an electron sink to affect catalyst-electrolyte interfacial reversible chemisorption of the oxygen species, which is expected to facilitate the oxidation of Co3+/Co4+. On the other hand, Au is helpful for the formation of the OOH intermediate by the "spillover effect".7. The NiCo2O4nanoarray was used as a template to further grow the NiCo2O4@NiO hybrid arrays. Such integrated electrodes exhibit an ultrahigh supercapacitive performance. The charge storage capacity of this hybrid was2220F/g at a current density of1A/g. With charging-discharging rate increasing from1to20A/g, NiCo2O4@NiO only show a～26.7%Csp loss. It is found that, the NiCo2O4@NiO hybrid array also showed a good cycling stability (6.7%capacitance loss over1000cycles).