Carbon dioxide transformation to fuels or chemicals provides an attractive approach for its utilization as feedstock and its emission reduction. Herein, we report a gas-phase electrocatalytic reduction of CO2 in an electrolytic cell, constructed using phosphoric acid-doped polybenz- imidazole （PBI） membrane, which allowed operation at 170 ℃ Pt/C and PtMo/C with variable ratio of Pt/Mo were studied as the cathode catalysts. The results showed that PtMo/C catalysts significantly enhanced CO formation and inhibited CH4 formation compared with Pt/C catalyst. Characterization by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy revealed that most Mo species existed as MoO3 in PtMo/C catalysts and the interaction between Pt and MoOx was likely responsible for the enhanced CO formation rate although these bicomponent catalysts in general had a larger particle size than Pt/C catalyst.
Dunfeng GaoFan CaiQinqin XuGuoxiong WangXiulian PanXinhe Bao
Nitrogen-doped carbon materials encapsulating 3 d transition metals are promising alternatives to replace noble metal Pt catalysts for efficiently catalyzing the oxygen reduction reaction(ORR). Herein, we use cobalt substituted perfluorosulfonic acid/polytetrafluoroethylene copolymer and dicyandiamide as the pyrolysis precursor to synthesize nitrogen-doped carbon nanotube(N–CNT) encapsulating cobalt nanoparticles hybrid material. The carbon layers and specific surface area of N–CNT have a critical role to the ORR performance due to the exposed active sites, determined by the mass ratio of the two precursors. The optimum hybrid material exhibits high ORR activity and stability, as well as excellent performance and durability in zinc–air battery.
Haihua WuXiaole JiangYifan YeChengcheng YanSonghai XieShu MiaoGuoxiong WangXinhe Bao
The orientation control of graphene overlayers on metal surface is an important issue which remains as a challenge in graphene growth on Ni surface. Here we have demonstrated that epitaxial graphene overlayers can be obtained by annealing a nickel carbide covered Ni(111)surface using in situ surface imaging techniques. Epitaxial graphene islands nucleate and grow via segregation of dissolved carbon atoms to the top surface at about 400 °C.This is in contrast to a mixture of epitaxial and non-epitaxial graphene domains grown directly on Ni(111) at540 °C. The different growth behaviors are related to the nucleation dynamics which is controlled by local carbon densities in the near surface region.
Graphene layers are often exposed to gaseous environments in their synthesis and application processes, and interactions of graphene surfaces with molecules particularly H2 and O2 are of great importance in their physico-chemical properties. In this work, etching of graphene overlayers on Pt（111） in H2 and O2 atmospheres were investigated by in-situ low energy electron microscopy. Significant graphene etching was observed in 10-5 Torr H2 above 1O23 K, which occurs simultaneously at graphene island edges and interiors with a determined reaction barrier at 5.7 eV. The similar etching phenomena were found in 10 7 Torr O2 above 973 K, while only island edges were reacted between 823 and 923 K. We suggest that etching of graphene edges is facilitated by Pt-aided hydrogenation or oxidation of edge carbon atoms while intercalation-etching is attributed to etching at the interiors at high temperatures. The different findings with etching in O2 and H2 depend on competitive adsorption, desorption, and diffusion processes of O and H atoms on Pt surface, as well as intercalation at the graphene/Pt interface.
Co-electrolysis of CO2and H2O using high-temperature solid oxide electrolysis cells(SOECs) into valuable chemicals has attracted great attentions recently due to the high conversion and energy efficiency,which provides opportunities of reducing CO2emission, mitigating global warming and storing intermittent renewable energies. A single SOEC typically consists of an ion conducting electrolyte, an anode and a cathode where the co-electrolysis reaction takes place. The high operating temperature and difficult activated carbon-oxygen double-bond of CO2put forward strict requirements for SOEC cathode. Great efforts are being devoted to develop suitable cathode materials with high catalytic activity and excellent long-term stability for CO2/H2O electro-reduction. The so far cathode material development is the key point of this review and alternative strategies of high-performance cathode material preparation is proposed. Understanding the mechanism of CO2/H2O electro-reduction is beneficial to highly active cathode design and optimization. Thus the possible reaction mechanism is also discussed. Especially, a method in combination with electrochemical impedance spectroscopy(EIS) measurement, distribution functions of relaxation times(DRT) calculation, complex nonlinear least square(CNLS) fitting and operando ambient pressure X-ray photoelectron spectroscopy(APXPS) characterization is introduced to correctly disclose the reaction mechanism of CO2/H2O co-electrolysis. Finally, different reaction modes of the CO2/H2O coelectrolysis in SOECs are summarized to offer new strategies to enhance the CO2conversion. Otherwise,developing SOECs operating at 300-600 °C can integrate the electrochemical reduction and the Fischer-Tropsch reaction to convert the CO2/H2O into more valuable chemicals, which will be a new research direction in the future.
Hexagonal β-Co(OH)2 nanosheets with edge length of 50 nm and thickness of 10 nm were hydrothermally synthesized with the aid of triethylamine.Upon calcination at 350°C in air,the β-Co(OH)2 nanosheets was converted into Co3O4 nanosheets with a similar dimension.Structural analyses during the calcination process identified that the β-Co(OH)2 precursor was initially dehydrated to HCoO2 and subsequently transferred into Co3O4.When being applied to catalyze CO oxidation at room temperature,the Co3O4 nanosheets exhibited a higher activity than the conventional spherical nanoparticles.This was perhaps related to the partial exposure of the{112}planes over the Co3O4 nanosheets.The porous structure generated during the calcination process also provided significant amounts of surface defects,which might contribute to the enhanced catalytic activity as well.
