The Influence of Porous Co/CeO1.88-Nitrogen-Doped Carbon Nanorods on the Specific Capacity of Li-O2 Batteries.

Li-O2 batteries are attracting considerable attention as a promising power source for electric vehicles as they have the highest theoretical energy density among reported rechargeable batteries. However, the low energy density and efficiency of Li-O2 batteries still act as limiting factors in real cell implementations. This study proposes the cathode structure engineering strategy by tuning the thickness of a catalyst layer to enhance the Li-O2 battery performance. The construction of the Li-O2 battery with a thinner porous cathode leads less parasitic reactions at the solid electrolyte interface, maximization of the catalyst utilization, and facile transport of oxygen gas into the cathode. A remarkably high specific capacity of 33,009 mAh g-1 and the extended electrochemical stability for 75 cycles at a 1000 mAh g-1 limited capacity and 100 mA g-1 were achieved when using the porous Co/CeO1.88-nitrogen-doped carbon nanorod cathode. Further, a high discharge capacity of 20,279 mAh g-1 was also achieved at a relatively higher current density of 300 mA g-1. This work suggests the ideal cathode structure and the feasibility of the Co/CeO1.88-nitrogen-doped carbon nanorod as the cathode material, which can minimize the areal cathode catalyst loading and maximize the gravimetric energy density.

Pulse Electrodeposition of a Superhydrophilic and Binder-Free Ni-Fe-P Nanostructure as Highly Active and Durable Electrocatalyst for Both Hydrogen and Oxygen Evolution Reactions.

Development and fabrication of electrodes with favorable electrocatalytic activity, low-cost, and excellent electrocatalytic durability are one of the most important issues in the hydrogen production area using the electrochemical water splitting process. We use the pulse electrodeposition method as a versatile and cost-effective approach to synthesize three-dimensional Ni-Fe-P electrocatalysts on nickel nanostructures under various applied frequencies and duration times, in which nanostructures exhibit excellent intrinsic electrocatalytic activity. Benefiting from the three-dimensional structure, as well as the simultaneous presence of the three elements nickel, iron, and phosphorus, the electrode fabricated at the optimal conditions has indicated outstanding electrocatalytic activity with a η10 of 66 and 198 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, in a 1.0 M KOH solution. Also, the water electrolysis cell constructed with this electrode and tested as a bifunctional electrode exhibited 1.508 V for 10 mA cm-2 in overall water splitting. In addition, the lowest amount of potential change in 100 mA cm-2 was observed for HER and OER, indicating excellent electrocatalytic stability. This study proposes a binder-free and economical technique for the synthesis of three-dimensional electrocatalysts.

Pd nanoparticles deposited on Co(OH)2 nanoplatelets as a bifunctional electrocatalyst and their application in Zn-air and Li-O2 batteries.

The development of affordable electrocatalysts for both oxygen reduction and evolution reactions (ORR/OER) has received great interest due to their importance in metal-air batteries and regenerative fuel cells. We developed a high-performance bifunctional oxygen electrocatalyst based on Pd nanoparticles supported on cobalt hydroxide nanoplatelets (Pd/Co(OH)2) as an air cathode for metal-air batteries. The Pd/Co(OH)2 shows remarkably higher electrocatalytic activity in comparison with commercial catalysts (Pt/C, IrO2), including an ORR half-wave potential (E1/2) of 0.87 V vs. RHE and an OER overpotential of 0.39 V at 10 mA cm-2 in aqueous alkaline medium. The Zn-air battery constructed with Pd/Co(OH)2 presents stable charge/discharge voltage (ΔEOER-ORR = 0.69 V), along with durable cycling stability for over 30 h. Also, this cathode exhibits a maximum discharge capacity of 17 698 mA h g-1, and stable battery operation over 50 cycles at a fixed capacity of 1000 mA h g-1, as an efficient air electrode for Li-O2 batteries, indicating that Pd/Co(OH)2 can be a potential candidate for both aqueous and non-aqueous metal-air batteries.

Electrodeposition of Ni-Co-Fe mixed sulfide ultrathin nanosheets on Ni nanocones: a low-cost, durable and high performance catalyst for electrochemical water splitting.

The development of a bi-functional active and stable catalyst for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is an important challenge in overall electrochemical water splitting. In this study, firstly, nickel nanocones (NNCs) were formed using electrochemical deposition, and then Ni-Co-Fe based mixed sulfide ultrathin nanosheets were obtained by directly depositing on the surface of the nanocones using the CV method. With a hierarchical structure of Ni-Fe-Co-S nanosheets, not only was a high active surface area created, but also the electron transfer and mass transfer were enhanced. This structure also led to the faster release of hydrogen bubbles from the surface. An overpotential value of 106 mV was required on the surface of this electrode to generate a current density of 10 mA cm-2 in the HER, whereas, for the OER, 207 mV overpotential was needed to generate a current density of 10 mA cm-2. Furthermore, this electrode required 1.54 V potential to generate a current density of 10 mA cm-2 in the total electrochemical water splitting. The resulting electrode also exhibited reasonable electrocatalytic stability, and after 10 hours of electrolysis in the overall water splitting reaction, the voltage change was negligible. This study introduces a simple, efficient, reasonable and cost-effective method of creating an effective catalyst for the overall water splitting process.

Hierarchical Nickel-Cobalt Dichalcogenide Nanostructure as an Efficient Electrocatalyst for Oxygen Evolution Reaction and a Zn-Air Battery.

A unique three-dimensional (3D) structure consisting of a hierarchical nickel-cobalt dichalcogenide spinel nanostructure is investigated for its electrocatalytic properties at benign neutral and alkaline pH and applied as an air cathode for practical zinc-air batteries. The results show a high oxygen evolution reaction catalytic activity of nickel-cobalt sulfide nanosheet arrays grown on carbon cloth (NiCo2S4 NS/CC) over the commercial benchmarking catalyst under both pH conditions. In particular, the NiCo2S4 NS/CC air cathode shows high discharge capacity, a narrow potential gap between discharge and charge, and superior cycle durability with reversibility, which exceeds that of commercial precious metal-based electrodes. The excellent performance of NiCo2S4 NS/CC in water electrolyzers and zinc-air batteries is mainly due to highly exposed electroactive sites with a rough surface, morphology-based advantages of nanosheet arrays, good adhesion between NiCo2S4 and the conducting carbon cloth, and the active layer formed of nickel-cobalt (oxy)hydroxides during water splitting. These results suggest that NiCo2S4 NS/CC could be a promising candidate as an efficient electrode for high-performance water electrolyzers and rechargeable zinc-air batteries.

Chrysanthemum flower-like NiCo2O4-nitrogen doped graphene oxide composite: an efficient electrocatalyst for lithium-oxygen and zinc-air batteries.

Chrysanthemum flower-like NiCo2O4-nitrogen doped graphene oxide composite material has been explored as a bifunctional cathode electrocatalyst for aqueous zinc-air and non-aqueous lithium-oxygen batteries. This cathode exhibits maximum discharge capacities of 712 and 15 046 mA h g-1 for zinc-air and lithium-oxygen batteries, respectively, with stable cycling over 50 cycles.