Development of efficient electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) remain key issues for the commercialization of fuel cells and metal–air ...batteries. In this study, A CoFe2O4/graphene nanohybrid is facilely synthesized via a two-step process and applied as an electrocatalyst for the ORR and the OER. The as-prepared CoFe2O4/graphene nanohybrid demonstrates excellent catalytic activity for the ORR. At the same mass loading, the Tafel slope of CoFe2O4/graphene electrocatalyst for the ORR is comparable to that of the commercial Pt/C (20 wt% Pt on Vulcan XC-72, Johnson Matthey). The ORR on CoFe2O4/graphene mainly favours a direct 4e− reaction pathway. The CoFe2O4/graphene nanohybrid also affords high catalytic activity for the OER. The chronoamperometric tests show that CoFe2O4/graphene catalyst exhibits excellent stability for both the ORR and the OER, outperforming the commercial Pt/C. The high electrocatalytic activity and durability of CoFe2O4/graphene nanohybrid are attributed to the strong coupling between CoFe2O4 nanoparticles and graphene.
•A CoFe2O4/graphene nanohybrid is facilely synthesized.•CoFe2O4/graphene nanohybrid is an efficient bi-functional electrocatalyst for the ORR and the OER.•CoFe2O4/graphene nanohybrid could be used as a potential catalyst for metal–air batteries.
The exploring of catalysts with high‐efficiency and low‐cost for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the key issues for many renewable energy systems ...including fuel cells, metal–air batteries, and water splitting. Despite several decades pursuing, bifunctional oxygen catalysts with high catalytic performance at low‐cost, especially the one that could be easily scaled up for mass production are still missing and highly desired. Herein, a hybrid catalyst with NiCo alloy nanoparticles decorated on N‐doped carbon nanofibers is synthesized by a facile electrospinning method and postcalcination treatment. The hybrid catalyst NiCo@N‐C 2 exhibits outstanding ORR and OER catalytic performances, which is even surprisingly superior to the commercial Pt/C and RuO2 catalysts, respectively. The synergetic effects between alloy nanoparticles and the N‐doped carbon fiber are considered as the main contributions for the excellent catalytic activities, which include decreasing the intrinsic and charge transfer resistances, increasing CC, graphitic‐N/pyridinic‐N contents in the hybrid catalyst. This work opens up a new way to fabricate high‐efficient, low‐cost oxygen catalysts with high production.
NiCo alloy nanoparticles decorated on N‐doped carbon nanofibers as a highly active and durable oxygen electrocatalyst at low‐cost are synthesized and reported. The hybrid catalyst with suitable amount of NiCo alloy nanoparticles loading (NiCo@N‐C 2) gives the most outstanding oxygen reduction reaction and oxygen evolution reaction electrocatalytic performances, which is even surprisingly superior to the commercial Pt/C and RuO2 catalysts, respectively.
An urchin-like La0.8Sr0.2MnO3 (LSM) perovskite oxide has been synthesized through a co-precipitation method with urea as a precipitator, and characterized by thermogravimetric analysis (TGA), X-ray ...diffraction (XRD), scanning electron microscopy (SEM) and BET analysis. SEM results show that a micro/nanocomposite with an urchin-like morphology has been obtained. The as-synthesized LSM perovskite oxide has a high specific surface area of 48 m2 g−1. The catalytic activity of the oxide for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in 0.1 M KOH solution has been studied by using a rotating-ring-disk electrode (RRDE). In the ORR test, a maximum cathodic current density of 5.2 mA cm−2 at −1.0 V (vs. Ag/AgCl) with 2500 rpm was obtained, and the ORR mainly favors a direct four-electron pathway. The results of anodic linear scanning voltammograms indicate that the urchin-like LSM perovskite oxide exhibits an encouraging catalytic activity for the OER. All electrochemical measurements suggest that the urchin-like LSM perovskite oxide could be used as a bifunctional catalyst for the ORR and the OER.
•Urchin-like La0.8Sr0.2MnO3 (LSM) perovskite oxide has been synthesized.•Mechanism of the ORR on urchin-like LSM perovskite oxide has been studied.•Urchin-like LSM perovskite oxide is a bifunctional catalyst for the ORR and the OER.•Urchin-like LSM perovskite oxide could be used as a potential catalyst for a lithium-air battery.
A lithium ion battery electrode is a composite of active material, polymeric binder, and conductive carbon additive(s). Cooperation among the different components plays a subtle and important role ...in determining the physical and electrochemical properties of the electrode. In this study, the physical and electrochemical properties of a LiNi0.8Co0.15Al0.05O2 cathode were investigated as a function of the electrode compositions. The electrode conductivity, porosity, specific capacity, first Coulombic efficiency, and rate capability were found significantly affected by the polyvinylidene difluoride (PVDF)-to-acetylene black (AB) ratio and the total inactive material amount. The electronic conductivity of the laminate does not so much decide the rate performance of the electrode as it is generally believed. The rate capability of the electrode is enhanced by an increase in the total inactive material content at a PVDF/AB ratio of 5:4, whereas it is deteriorated by increasing the total inactive material content at PVDF/AB ratios of 5:1 and 5:2. At a PVDF/AB ratio of 5:3, the rate performance is not considerably affected by the inactive material content. The result is explained by the competition between the ion-blocking effect of PVDF binder and the electronic conducting effect of the AB additive. A long-term cycling experiment shows the mechanical integrity of the laminate is important for the durability of the composite electrode.
Lithium-air battery has attracted extensively attention and now developing catalysts with high electrocatalytic activity is one of the challenges for lithium-air battery. In this paper, 3D ...hierarchical porous spinel CoFe2O4 hollow nanospheres were first prepared by a facile hydrothermal method. The hollow CoFe2O4 nanospheres have unique bimodal porous structure which consists of micropores and mesopores. The catalytic activity of the CoFe2O4 hollow nanospheres for oxygen reduction reaction (ORR) has been studied and compared with the acetylene black, the solid CoFe2O4 nanospheres and the commercial Pt/C by using rotating ring-disk electrode (RRDE) technique. The spinel CoFe2O4 hollow nanospheres exhibit superior catalytic activity for the ORR compared to the acetylene black and the solid CoFe2O4 nanospheres. Besides, the spinel CoFe2O4 hollow nanospheres also afford high catalytic activity for the oxygen evolution reaction (OER). Furthermore, the hollow CoFe2O4 nanospheres show the smallest overpotential between ORR and OER. The chronoamperometric studies show that the CoFe2O4 hollow nanospheres exhibit excellent stability for both the ORR and OER. The high ORR and OER activities and stabilities of CoFe2O4 hollow nanospheres could be attributed to their special 3D hierarchical porous structure. This material shows a significant potential application on lithium-air battery.
High efficient, cost-effective catalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the key issue of the rechargeable lithium-air batteries. Herein, we ...report the facile synthesis of hierarchical NiCo2O4 (NCO) hollow nanospheres via a hard template method and following heat treatment. The synthesized hollow NCO consists of ultrathin nanosheets, which could provide larger specific surface area, more active sites and easy access channels for oxygen and electrolyte transport. The electrochemical studies reveal that the NCO hollow owns excellent ORR and OER catalytic activities, characterized with lower onset potential, higher diffusion limiting current density. Moreover, the NCO hollow shows superior stability compared to that of NCO urchin, Pt/C and RuO2 for ORR and OER, respectively. The excellent electrocatalytic activities, long-term stability for both the ORR and OER and the facile synthesis procedure make the NCO hollow a potential promising bi-functional catalyst for the metal-air batteries and fuel cells.
•Hierarchical NiCo2O4 hollow nanospheres have been prepared via a hard template method.•The synthesized NCO hollow consists of ultrathin nanosheets.•The NCO hollow exhibits excellent catalytic activity for both ORR and OER.•The NCO hollow also owns superior long-term stability.
Ba0.5Sr0.5Co0.8Fe0.2O3 perovskite oxide has been synthesized by a sol–gel method, and characterized by XRD, SEM, BET. This oxide has a porous structure and a specific surface area of 2.78 m2 g−1. The ...catalytic activity of the oxide for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that the ORR mainly favors a direct four electron pathway, and a maximum cathodic current density of 6.25 mA cm−2 at 2500 rpm was obtained, which is close to the behavior of Pt/C (20 wt% Pt on carbon) electrocatalyst in the same testing conditions. Compared with pure C electrode, BSCF is more active for OER, a lower onset potential for OER and a bigger anodic current at the same applied potential are observed.
•BSCF was evaluated as bifunctional catalyst in alkaline media.•A maximum current density of 6.25 mA cm−2 at 2500 rpm was obtained for the ORR.•The ORR mainly favors a direct four electron pathway.•BSCF had better catalytic activity for the OER than that of the pure C electrode.
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