Yudong Xue

Tuning α-Fe2O3 nanotube arrays for the oxygen reduction reaction in alkaline media

The oxygen reduction reaction plays a crucial role in alkaline fuel cells. Herein, an α-Fe2O3 nanotube array material was fabricated via a facile two-step electrochemical anodization method and employed as an efficient ORR catalyst in alkaline media. Due to its highly ordered open top architecture, the α-Fe2O3 nanotube array electrode exhibits excellent ORR catalytic activity with an onset potential of −0.39 V (vs. Hg/HgO) and high current density of 6.95 mA cm−2. Results show that the ORR exhibits quasi-reversible diffusion-controlled reaction characteristics and a well-defined four electron pathway. Moreover, as the crystalline structure transforms from α-Fe2O3 to Fe3O4 or as the alkaline concentration increases, the ORR activity is disturbed and the electron transfer number decreases. The as-prepared electrodes possess favorable alkaline tolerance as indicated from their chronoamperometric curves and Raman spectra. Accordingly, this novel α-Fe2O3 nanotube array material can be employed as efficient and low cost non-noble metal electrodes for electrochemical energy applications.

Hierarchical oxygen-implanted MoS2 nanoparticle decorated graphene for the non-enzymatic electrochemical sensing of hydrogen peroxide in alkaline media

Owing to the extensive applications of hydrogen peroxide (H2O2) in biological, environmental and chemical engineering, it is of great importance to investigate sensitive and selective sensing platform towards the detection of H2O2. Herein, oxygen-implanted MoS2 nanoparticles decorated graphene nanocomposite is synthesized via a facile one-pot solvothermal method for the sensitive detection of H2O2 in alkaline media. The structure and morphology of the MoS2/graphene nanocomposites were systematically characterized, showing that Mo-O bonds are formed and oxygen is implanted into the crystal structure in the nanocomposite. As a result, the MoS2/graphene composite exhibited enhanced electron transfer kinetics and excellent electro-reduction performance towards H2O2 in alkaline media. Under optimum conditions, the fabricated sensor demonstrated a wide linear response towards H2O2 in the range of 0.25-16mM with a low detection limit of 0.12μM and high sensitivity of 269.7μAmM-1cm-2. Besides, the constructed sensor presented a good selectivity to H2O2 with the presence of other interfering species. Therefore, the proposed sensor was successfully applied for the detection and determination of H2O2 in real sample, indicating great potential for the practical applications.

Low-temperature CO oxidation over integrated penthorum chinense-like MnCo2O4 arrays anchored on three-dimensional Ni foam with enhanced moisture resistance

Advanced integrated nanoarray (NA) catalysts have been designed by growing metal-doped Co3O4 arrays on nickel foam with robust adhesion. Ternary MCo2O4 NA catalysts were prepared by doping urchin-like Co3O4 with different transition metals (Cu2+, Mn2+, Fe2+, Ni2+, Zn2+, Fe3+ and Al3+). These catalysts exhibited novel morphologies and can be directly applied as monolithic materials for CO oxidation. Among the MCo2O4 NA catalysts, CuCo2O4 nanoneedles manifested the highest catalytic activity in dry air, achieving an efficient 100% CO oxidation conversion of 20 000 h−1 at 146 °C, due to its reducibility at lower temperature, lattice distortion of the spinel structure, and abundant surface-adsorbed oxygen (Oads). The doped catalytic systems were further optimized by controlling the volume ratio of reactive components in the mixed solvent, the Cu or Mn contents to determine excellent catalysts for direct application to CO oxidation at 1.0 vol% moisture. Penthorum chinense-like MnCo2O4 NAs showed optimal catalytic performance at 1 vol% moisture (T100 = 175 °C), with activity higher than that of the CuCo2O4 NA catalyst, indicating that the synergistic effect between MnOx and Co3O4 improved the moisture resistance and stability. It was concluded that the moisture resistance provided by introducing active sites on Co-based catalysts decreased as follows: Mn sites > Co sites > Cu sites > Ni sites. MCo2O4 NAs, with predominantly exposed {110} surfaces, showed higher catalytic activity than catalysts with exposed {111} surfaces. This study suggests that the as-prepared MnCo2O4 NAs anchored on 3D Ni foam with remarkable moisture resistance have potential applications in CO oxidation.

W-doped MoS2 nanosheets as a highly-efficient catalyst for hydrogen peroxide electroreduction in alkaline media

Novel W-doped MoS2 electrocatalysts have been successfully fabricated through a facile one-pot solvothermal method and employed for the hydrogen peroxide reduction reaction (HPRR) in emerging alkaline H2O2-based fuel cells. The wide composition stoichiometry of W-doped MoS2 is obtained in molar fractions of 30% and 15%. It has been found that 30% W-doped MoS2 presents superior catalytic activity with a high peak current density of 2.83 mA cm−2 at −0.86 V vs. Hg/HgO, owing to the heteroatom doping and the defect sites that emerged in the nanostructure. Furthermore, the influence of alkali concentration, H2O2 concentration and temperature on the HPRR is systematically investigated. The mechanism of HPRR is illustrated using a rotating disk electrode as a direct two-electron electroreduction pathway. Thereby, a new insight into heteroatom doping in transition metal dichalcogenides for HPRR applications is provided.

Tunable nano-interfaces between MnOx and layered double hydroxides boost oxygen evolving electrocatalysis

The development of low overpotential, non-precious metal oxide electrocatalysts is important for sustainable water oxidation using renewable energy. Here we report the fabrication of nano-interfaces between MnOx nanoscale islands and NiFe layered double hydroxide (LDH) nanosheets, which were chosen as baseline electrocatalysts for OER activity tuning. The MnOx nano-islands were grown on the surfaces of NiFe-LDH nanosheets by atomic layer deposition (ALD). Morphological and structural characterization indicated that the MnOx formed flat nanoscale islands which uniformly covered the surfaces of NiFe-LDH nanosheets, giving rise to a large density of three-dimensional nano-interfaces at the NiFe-LDH/MnOx/electrolyte multi-phase boundaries. We showed by X-ray spectroscopic characterization that these nano-interfaces induced electronic interactions between NiFe-LDH nanosheets and MnOx nano-islands. Through such modifications, the Fermi level of the original NiFe-LDH was lowered by donating electrons to the MnOx nano-islands, dramatically boosting the OER performance of these electron-deficient NiFe-LDH catalysts. Using only 10 cycles of ALD MnOx, the MnOx/NiFe-LDH nanocomposites exhibited remarkable and enhanced electrocatalytic activity with an overpotential of 174 mV at 10 mA cm−2. This work demonstrates a promising pathway for tuning transition metal electrocatalysts via a generic ALD surface modification technique.

Integrated Cobalt Oxide Based Nanoarray Catalysts with Hierarchical Architectures: In Situ Raman Spectroscopy Investigation on the Carbon Monoxide Reaction Mechanism

Herein, a facile strategy for the in situ growth of a Co3O4‐based precursor with unique hierarchical architectures oriented diagonal or perpendicular to Ni surfaces is reported. This strategy to prepare grafted ZIF‐67@Co3O4 and MOF‐199@Co3O4 precursor structures is based on a simple hydrothermal synthesis method to obtain the Co3O4 precursor and the subsequent in situ growth of ZIF‐67 and MOF‐199, respectively. The morphologies of the Co3O4 products can be tailored by controlling the solvent polarity and concentration of precipitants. CO is chosen as a probe molecule to evaluate the catalytic performance of the as‐synthesized Co3O4‐based oxide catalysts, and the structure–activity relationships are confirmed by using TEM, H2 temperature‐programmed reduction, X‐ray photoelectron spectroscopy, Raman spectroscopy and in situ Raman spectroscopy, and extended X‐ray absorption fine structure analysis. These analysis results demonstrate that irislike Co3O4 exhibits a high catalytic activity for CO oxidation and contains an abundance of surface defect sites (Co3+ species) to result in an excellent low‐temperature reducibility, oxygen vacancies and unsaturated chemical bonds on the surface. Moreover, we used in situ Raman spectroscopy to record the structural transformation of Co3O4 directly during the reaction, which confirmed that CO oxidation on the surface of Co3O4 can proceed through the Langmuir–Hinshelwood mechanism (<200 °C) and the Mars–van Krevelen mechanism (>200 °C).