Research on catalysis for fuel cells is extremely important to enhance the sluggish oxygen reduction reaction (ORR) using heterogeneous catalyst materials. In this work, cobalt carbide (Co2C) and cobalt nitride (Co4N) nanoparticles were intercalated with reduced graphene oxide (rGO) sheets through heteroatom doping and utilized for the ORR in alkaline fuel cells, in which rGO acted as a catalyst support. Cyclic voltammetry results indicated that the ORR half-wave potentials of Co2C/rGO and Co4N/rGO were found to be −0.095 V and −0.118 V, respectively. Chronoamperometric studies revealed the excellent catalytic stability of the prepared catalysts. The reaction kinetics study showed that Co2C/rGO and Co4N/rGO pursued a 4e− (four electron) oxygen reduction process. The catalytic activity and stability in alkaline electrolyte indicated that Co2C/rGO and Co4N/rGO have great potential as alternatives to precious metal-based catalysts.

•Synthesized TiO2/rGO hybrid by a simple hydrolysis method.•The TiO2/rGO hybrid showed higher electrocatalytic activity and better stability.•The ORR of the TiO2/rGO hybrid following a 4-electron process.To overcome the shortcomings of high cost and rare sources of precious metal based catalysts, the catalytic characteristics of reduced graphene oxide (rGO) supported (N, F)-co-doped TiO2 hybrid (TiO2/rGO) for oxygen reduction are investigated. Results show that the onset potential of oxygen reduction reaction (ORR) under the catalysis of TiO2/rGO is about −0.20 V (vs. Hg/Hg2Cl2). The corresponding electron transfer number of ORR is 3.98, which means that the ORR is major happened through a 4-electron process. TiO2/rGO catalyst has high catalytic for ORR and better stability than the commercial Pt/C catalytic performance in alkaline electrolyte. TiO2/rGO catalyst shows great promise as a high activity non-precious metal catalyst for ORR.

•Cr2O3, which is usually adopted as ceramic material, is doped as catalyst for oxygen reduction.•Transitional metal oxide with low cost and rich sources is employed as catalysts for oxygen reduction.•4-electron style oxygen reduction reaction is observed with the catalysis of Cr2O3.Reduced graphene oxide (rGO) supported nano-chromium oxide (Cr2O3/rGO) catalyst for oxygen reduction reaction (ORR) has been successfully synthesized by the pyrolysis of chromium-urea coordination compound. The structure and morphology of the hybrid are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) tests. XRD tests reveal that the Cr2O3 with hexagonal structure is obtained. SEM and TEM tests show that the nano-Cr2O3 is supported by rGO sheet. The cyclic voltammetry, tafel, linear scanning voltammetry and current-time chronoamperometric tests prove that the obtained Cr2O3/rGO hybrid has a remarkable catalytic activity and good stability for oxygen reduction. Both the rotating disc electrode and rotating ring disc electrode tests approve that the ORR major happens through 4-electron reaction style. The Cr2O3/rGO hybrid is a promising low cost and high performances catalyst for ORR of alkaline electrolyte.

•Mn2O3 is doped to MnO to improve the catalytic performances.•Transition metal oxides with low cost and rich sources are potential catalysts for oxygen reduction.•The doping of Mn2O3 to MnO enhanced the 4-electron oxygen reduction reaction.In this study, the catalyst of reduced graphene oxide (rGO) supported Mn2O3 doped MnO for oxygen reduction reaction (ORR) has been successfully synthesized. The structures and morphology of the Mn2O3 doped MnO were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). XRD tests reveal that the Mn2O3 is successfully doped to MnO. The cyclic voltammetry, Tafel, linear scanning voltammetry and current-time chronoamperometric tests prove that the Mn2O3 doped MnO has a better catalytic performance and stronger stability than pure MnO for oxygen reduction. Both the rotating disc electrode and rotating ring disc electrode tests approve that the ORR happens mainly through 4-electron reaction mechanism on Mn2O3 doped MnO. The ORR happens mainly through 2-electron reaction mechanism with the catalysis of pure MnO. The coexistence of manganese ions with different valent promotes the catalytic performance of metal oxide for oxygen reduction.

•Hydrogen storage characteristics of non-stoichiometric TiCrMo alloys were reported.•Hydrogen induce phase changes during the course of activation were investigated.•Hydrogenation induced morphology changes were observed by SEM tests.The influence of the partial substitution of Mo for Cr on phase composition and hydrogen storage characteristics of non-stoichiometric Laves phase TiCrB0.9-based alloys is investigated by X-ray diffraction (XRD), pressure composition isotherm (PCT), and scanning electron microscopy (SEM) characterizations. XRD tests reveal that the phase composition of the alloys gradually changes from single TiB1.07CrB1.93 Laves phase to the co-existence of Laves phase and Mo-based BCC phase with increasing substitution of Mo for Cr. The phase composition eventually transforms into a single Mo-based BCC phase when the amount of the substitution surpasses a certain level. PCT tests reveal that the maximum hydrogen storage capacity increases with increasing Mo content. The hydrogenation-induced phase changes are also greatly influenced by the substitution of Mo for Cr. SEM tests of the hydrided alloys show that the increasing Mo content enhances hydrogenation-induced pulverization. Finally, hydrogenation-induced phase changes during the course of activation are also investigated.

La0.78Mg0.22Ni3.48Co0.22Cu0.12 alloy is one kind of nonstoichiometric AB3.5 type hydrogen storage alloy with low cost and high capacity. In this paper, the effect of annealing treatment on the structure and hydrogen absorption–desorption characteristics of the alloy is discussed. The annealing temperature is determined by using thermogravimetry–differential scanning calorimetry (TG–DSC) tests. The structure of as-cast and annealed alloys is examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results show that the crystal cell volume decreases after annealing treatment. SEM tests reveal that the structure of the annealed alloys is more regular than that of the as-cast alloy. Influences of annealing treatment on maximum and reversible hydrogen storage capacity, hysteresis factor (Hf) between hydrogen absorption and desorption, sloping factor (Sf), enthalpy changes (ΔH) and entropy changes (ΔS) of hydrogen absorption are discussed in detail.Highlights► Temperature of annealing treatment was ascertained by TG–DSC tests. ► The structure of hydrogen storage alloy was homogenized by annealing treatment. ► The hydrogen absorbing plateau pressure was elevated by the decreased crystal cell volume. ► The hysteresis between hydrogen absorption and desorption were enhanced by annealing treatment despite the improvement of plateau performance.

In this paper, the structure, hydrogen storage performance, electrochemical discharge and cyclic characteristics of La0.7Mg0.3Ni3.2Co0.35−XCuX alloys were investigated using X-ray diffraction (XRD), pressure composition isotherm (PCT) and electrochemical tests. XRD tests showed that all of the alloys were composed of La2Ni7 and LaNi phases. The ratio of LaNi phase in these alloys increased with increasing substitution of Cu for Co. PCT tests showed that increasing substitution of Cu for Co resulted in the decrease of hydrogen storage capacity and the increase of plateau pressure. Electrochemical discharge tests showed that the discharge capacity increased first and then decreased with increasing substitution of Cu for Co.

In this paper, microstructure and hydrogen storage characteristics of TiMn2−XVX alloys were investigated by means of XRD, SEM, metallography and PCT tests. XRD tests showed that with the increase of V content the phase composition of these alloys changed from coexistent V based BCC phase and Laves phase to single V based BBC phase. Segregation of both V and Mn was weakened, simultaneously. Hydrogen storage capacity of these alloys increased with increasing V content. Both enthalpy change and entropy change of hydrogen absorption were augmented accompanied with the enhancement of hysteresis between hydrogen absorption and desorption.

•A facile methodology to dope nitrogen or/and boron to CNT is reported.•Nitrogen-boron co-doped CNT is a high performance catalyst for oxygen reduction.•The co-doped nitrogen and boron promote the 4-electron oxygen reduction reaction.•The exchange current intensity is enhanced by co-doped nitrogen and boron.In this paper, we designed a facile method to prepare nitrogen doped CNT (N-CNT), boron-doped CNT (B-CNT) and nitrogen, boron co-doped CNT (N,B-CNT) catalysts for oxygen reduction. The microstructures of the catalysts were characterized by Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS). The results clearly showed the successful doping of nitrogen or/and boron. The cyclic voltammetry (CV), Tafel, linear scanning voltammetry (LSV) tests confirmed that the onset potentials and peak current intensities of oxygen reduction increased in the sequence of pure CNT < N-CNT < B-CNT < N,B-CNT. The rotating disc electrode (RDE) tests proved the electron transfer number of oxygen reduction increased with the doping of nitrogen, boron and co-doping of nitrogen and boron. The N,B-CNT is a promising catalyst for oxygen reduction.Figure optionsDownload full-size imageDownload high-quality image (337 K)Download as PowerPoint slide

Research on catalysis for fuel cells is extremely important to enhance the sluggish oxygen reduction reaction (ORR) using heterogeneous catalyst materials. In this work, cobalt carbide (Co2C) and cobalt nitride (Co4N) nanoparticles were intercalated with reduced graphene oxide (rGO) sheets through heteroatom doping and utilized for the ORR in alkaline fuel cells, in which rGO acted as a catalyst support. Cyclic voltammetry results indicated that the ORR half-wave potentials of Co2C/rGO and Co4N/rGO were found to be −0.095 V and −0.118 V, respectively. Chronoamperometric studies revealed the excellent catalytic stability of the prepared catalysts. The reaction kinetics study showed that Co2C/rGO and Co4N/rGO pursued a 4e− (four electron) oxygen reduction process. The catalytic activity and stability in alkaline electrolyte indicated that Co2C/rGO and Co4N/rGO have great potential as alternatives to precious metal-based catalysts.