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Oxygen vacancy (OV)-rich solid-solution ruthenium manganese oxide nanowires (V-RuxMn1−xO2 NWs), synthesized by the hydrothermal reaction of metastable MnO2 nanosheets in the presence of RuCl3 with the use of CoCl2 as the OV producer, are reported to be efficient and stable catalysts for acidic oxygen evolution reaction (OER). They only need an overpotential of 200 mV to drive 10 mA cm−2 and show excellent durability for >600 h in 0.5 M H2SO4. Their mass activity is >35.9 times higher than that of commercial RuO2. The strong Ru–O–Mn bond interaction achieved by the solid solution structure and the OVs are the main origins of their high activity and excellent durability for the acidic OER. The Ru–O–Ru bonds are not favorable for the high catalytic activity of the V-RuxMn1−xO2 NWs. The DFT calculations indicate that both the strong Ru–O–Mn bond interaction and the OVs can decrease the energy barrier of the OER rate-determining step and suppress Ru demetallation, improving the catalytic activity and stability of the V-RuxMn1−xO2 NWs. A water electrolyzer with the V-RuxMn1−xO2 NWs exhibits a low voltage of 1.48 V to deliver 10 mA cm−2 and shows no obvious performance drop for >300 h at 10 mA cm−2, respectively. [ABSTRACT FROM AUTHOR]

The development of stable electrode materials with high specific capacities is of paramount importance for sodium-ion batteries (SIBs) to make them competitive with lithium-ion batteries (LIBs). This study reports the use of a Co-seed-mediated method for the synthesis of CNT-supported multiphase zero-valent Sb nanoparticles in the forms of Sb, CoSb, and CoSb2 with nitrogen-doped carbon coating (NC@CoSb/CNTs-400). The obtained NC@CoSb/CNTs-400 shows high capacities and excellent durability for sodium storage. It can exhibit high stable reversible capacities of 352.4 and 330.4 mA h g−1 at 0.1 and 1.0 A g−1, respectively, and deliver outstanding rate-capacities of 263.8 and 243.9 mA h g−1 at 5.0 and 10.0 A g−1, respectively. No obvious capacity drops are observed when it is sodiated/desodiated at 5.0 and 10.0 A g−1 for >10 000 cycles, respectively. Its superior performance arises from the unique structure. Specifically, the multiphase Sb NPs in the forms of Sb, CoSb, and CoSb2 increase the accessibility of Sb to sodium storage, improving the specific capacities of NC@CoSb/CNTs-400. The NC coating and CNT support increase the stability of NC@CoSb/CNTs-400, endowing it with excellent durability. [ABSTRACT FROM AUTHOR]

La/Fe co-doped Co3O4 nanoparticles supported on aminated carbon nanotubes (LaFe–Co3O4/NCNTs) have been demonstrated to be active bifunctional catalysts for oxygen reduction/revolution reactions (ORR/OER). With optimal La/Fe doping levels, LaFe–Co3O4/NCNTs exhibits an overall ORR/OER bifunctional catalytic activity higher than most catalysts reported recently. The high performance of LaFe–Co3O4/NCNTs mainly originates from the specific La/Fe co-doped structure of the LaFe–Co3O4 NPs, which increases both the ORR and OER catalytic activities of the LaFe–Co3O4 NPs to higher degrees. DFT calculations have shown that the La/Fe co-doping can decrease the overpotentials of both the ORR and the OER and increase the stability of the LaFe–Co3O4 NPs. Additionally, carbon coating can further increase the catalytic activities of LaFe–Co3O4/NCNTs by the decrease of the polarization losses caused by the electrical resistance. When used in zinc–air batteries (ZABs), the carbon coated LaFe–Co3O4/NCNTs (C@LaFe–Co3O4/NCNTs) can exhibit a maximum power density of 122.2 mW cm−2, which is >20% higher than that of mixed catalysts of Pt/C + RuO2. This, along with the much higher cycling stability of C@LaFe–Co3O4/NCNTs, suggests great potential for its use as a bifunctional catalyst for practical applications. [ABSTRACT FROM AUTHOR]

This work reports a novel in situ thermal exclusion approach for the synthesis of carbon coated Sb and Sb-doped SnO2 hetero-nanoparticles (Sb-ATO hetero-NPs) deposited on MWCNTs (C@Sb-ATO/MWCNTs) through the annealing of PPY@ATO/MWCNTs. Depending on the specific structural features of C@Sb-ATO/MWCNTs, which integrate the advantages of nanostructuring, elemental doping, heterostructuring, and carbon integration, C@Sb-ATO/MWCNTs shows improved performance for Na+ storage. Specifically, it exhibits a high reversible capacity (430.6 mA h g−1 at 0.1 A g−1), superior rate capabilities (198.5 mA h g−1 at 30.0 A g−1) and remarkable cycling stabilities (275.5 mA h g−1 at 5.0 A g−1 for up to 10 000 cycles). The Sb doping and Sb-ATO nanoheterostructuring are demonstrated to be the main origins of the high performance of C@Sb-ATO/MWCNTs. DFT calculations indicate that the Sb doping can increase the electrical conductivity of ATO and promote the diffusion and storage of Na+ ions in ATO, and the electrical conductivity of the Sb-ATO hetero-NPs can be further increased by the Sb-ATO heterostructuring. The result presented here indicates that the strategy in combination of nanostructuring, elemental doping, heterostructuring, and carbon integration is a promising way to obtain anode materials with high performance for Na+ storage. [ABSTRACT FROM AUTHOR]

Herein, a nitrogen doped carbon nanotube supported NiFe/NiSe2 heterostructure rich in oxygen vacancies (DBD-NiFe/NiSe2@NCNT) is successfully synthesized using atmospheric pressure dielectric barrier discharge plasma. It exhibits superior bifunctional catalytic activity towards the OER (η = 292 mV@10 mA cm−2) and ORR (E1/2 = 0.811 V), with a ΔE as low as 0.711 V in 0.1 M KOH electrolyte, outperforming most of the ones previously reported in the literature. Through physical structure characterization, electrochemical properties and DFT calculation studies, the unique heterostructure and oxygen vacancies/defects that synergistically promote the catalytic process and greatly improve the catalytic performance were verified. Impressively, the as-assembled rechargeable ZAB based on DBD-NiFe/NiSe2@NCNT as an electrocatalyst obtains a remarkable maximum power density of 131.61 mW cm−2 and an exceptional stability for 1000 cycles at 10 mA cm−2. Furthermore, the DBD-NiFe/NiSe2@NCNT-based flexible all-solid-state ZAB revealed excellent performance with robust flexibility. This work provides worthy insights into the search for high-efficiency and low-cost energy storage and conversion devices. [ABSTRACT FROM AUTHOR]

A plasma assisted phosphorization method has been developed for preparation of multi-phase materials with rich crystalline interfaces and oxygen vacancies. Specifically, P-NiMoP nanorods (NRs) comprising tri-phases of MoP2, Ni3P and MoO2 have been synthesized by plasma-assisted phosphorization of NiMoO4 NRs. The specific features of the plasma technique provide P-NiMoP NRs with rich crystalline interfaces and oxygen vacancies in MoO2. P-NiMoP NRs are demonstrated to be a stable and efficient catalyst for the hydrogen evolution reaction (HER). They only need overpotentials of 3 and 162 mV to drive current densities of 10 and 150 mA cm−2, both of which are lower than those of Pt/C. The DFT calculations indicate that the tri-phase structure with rich crystalline interfaces and oxygen vacancies plays an important role in the high catalytic activity of P-NiMoP NRs. It promotes a strong electronic coupling between MoP2, Ni3P and MoO2, which facilitates H2O adsorption and dissociation and reduces the ‖ΔGH*‖ value. [ABSTRACT FROM AUTHOR]

Proper control of the size and composition distribution and oxidation state of metal ions is of great importance to develop mixed transition metal oxides with advanced catalytic activities for oxygen reduction (ORR) and evolution reactions (OER), both of which are pivotal processes related to many renewable energy related technologies. Herein, a cation exchange reaction is employed for the synthesis of NixCo(3−x)O4 nanoparticles (NPs) supported on aminated carbon nanotubes (NixCo(3−x)O4/NH2-CNTs). The obtained NixCo(3−x)O4/NH2-CNTs shows an enhanced catalytic bifunctionality for the ORR and OER. Specifically, the NixCo(3−x)O4/NH2-CNTs can deliver ORR onset (Eonset) and half-wave potentials (E1/2) of 0.954 and 0.863 V vs. RHE, respectively, and only needs an overpotential of 386 mV to deliver a current density of 10 mA cm−2. The ORR catalytic activity of the NixCo(3−x)O4/NH2-CNTs is comparable to that of the Pt/C (with an Eonset and E1/2 of 0.964 and 0.858 V vs. RHE, respectively), while its OER activity is higher than that of RuO2/C. Additionally, the NixCo(3−x)O4/NH2-CNTs exhibits a potential difference of 0.764 V in the OER current density at 10 mA cm−2 and the ORR current density at 3 mA cm−2, which is lower than those of most state-of-the-art catalysts. Most interestingly, the Zn–air battery with the NixCo(3−x)O4/NH2-CNTs shows higher durability and performance than the batteries with Pt–RuO2/C (an integrated catalyst consisting of Pt/C and RuO2/C). These results clearly demonstrate that the NixCo(3−x)O4/NH2-CNTs is a durable and efficient bifunctional catalyst with great potential for practical applications. [ABSTRACT FROM AUTHOR]

MnO2 nanorods grown on reduced graphene oxide (MnO2-NR/rGO) have been synthesized through a hydrothermal treatment of the reaction product between KMnO4 and 2-(N-morpholino)ethanesulfonic acid in the presence of graphene oxide. When tested as an anode in a lithium-ion battery (LIB), the obtained MnO2-NR/rGO exhibits a significant enhancement in electrochemical performance, especially after being discharged/charged for 300 cycles. Characterization of the microscopic features suggests that the morphology and crystal structure of the MnO2 nanorods evolve gradually during cycling, transforming the product of the MnO2-NR/rGO into a unique electrode architecture consisting of well-separated rGO coated with well-crystallized λ-MnO2 after 300 cycles. The significantly enhanced electrochemical performance of the MnO2-NR/rGO electrode after 300 cycles is attributed mainly to the resulting electrode architecture, which enhances the interaction between MnO2 and rGO, reduces the charge transfer resistance across the MnO2/rGO interface, and makes the rGO readily accessible to lithium ion storage. The demonstrated specific capacity and rate capability are among the best ever reported for transition metal oxide based electrodes for LIBs. [ABSTRACT FROM AUTHOR]

The encapsulation of transition metal oxide (TMO) particles in a graphene hollow shell to form a core-void-shell structure is an attractive way to improve the electrochemical performance of TMO-based electrodes for lithium ion batteries (LIBs). First, the continuous graphene shell may enhance the electrical conductivity of the electrodes and thus facilitate current collection and charge transfer associated with lithium storage. Second, the unique shell structure may suppress the aggregation of the core TMO particles while the void space between the core and shell may accommodate the large volume changes of the core during charge–discharge cycling, which enhances electrode stability against cycling. Third, the high specific surface area may improve the accessibility of active electrode materials to the electrolyte, which could effectively reduce the solid-state diffusion length and thus enhance Li ion transport and rate capability. When tested in a LIB, a Fe3O4@rGO composite electrode exhibits an initial reversible capacity of 1236.6 mA h g−1, which is much higher than that of an electrode based on bare Fe3O4, a physical mixture of Fe3O4 and graphene, or other forms of Fe3O4 reported in the literature. In addition, the cycling performance and rate capacity are also much better. The results clearly demonstrate that this unique electrode architecture is ideally suited for LIBs and other electrochemical energy storage and conversion devices. [ABSTRACT FROM AUTHOR]

Amine functionalized holey graphene (AFHG), synthesized by the hydrothermal reaction of GO and ammonia and the subsequent KOH etching, has been used as a metal-free catalyst for the oxygen reduction reaction (ORR). It shows that AFHG is highly active for the ORR and exhibits higher electrocatalytic activity than graphene, nitrogen-doped graphene (NG) and amine functionalized graphene (AFG), which could be demonstrated from its higher current density and more positive half-wave and onset potentials for the ORR. Although AFHG also exhibits a slightly higher overpotential towards ORR, it is indeed more kinetically facile than the commercial JM Pt/C 40 wt%. Its higher electrochemical performance could be attributed to the presence of the electron donating group (e.g. amine) and a large number of holes in its sheet plate and the porous structure in its randomly stacked solid, which provide AFHG with higher electrical conductivity, more active edge N atoms and easier accessibility to oxygen, respectively. The stability measurements show that AFHG is more stable than graphene, NG, AFG and the JM Pt/C 40 wt% and exhibits higher immunity towards methanol crossover and CO poisoning than the JM Pt/C 40 wt%. Over 10 h of the ORR, AFHG loses only <7% of its original activity in the absence of methanol or CO, and the introduction of methanol or CO has no effect on its oxygen reduction activity, which makes it highly desirable as a metal-free catalyst for the ORR. [ABSTRACT FROM AUTHOR]