Boosting catalytic activity toward methanol oxidation reaction for platinum via heterostructure engineering

CuNi alloy anchored on dual-substrate TiOx/N-doped carbon nanofibers as a bifunctional electrocatalyst for rechargeable zinc-air batteries

Development of non-noble metal-based electrocatalysts to enhance the performance of zinc-air batteries (ZABs) is of great significance, but it remains a formidable challenge due to their poor stability and activity. Herein, a bifunctional CuNi-TiOx/NCNFS electrocatalyst, featuring with electron-rich copper-nickel (CuNi) alloy nanoparticles anchored on titanium oxide/N-doped carbon nanofibers (TiOx/NCNFS), is constructed by a dual-substrate loading strategy. The introduction of TiOx has led to a significant increase in the stability of the dual-substrate. The strong electronic interaction between CuNi and TiOx strengthens the anchoring of active metal sites, thus accelerating the electron transfer. Theoretical calculations unclose that NCNFS can regulate the charge distribution of TiOx, inducing the charge transfer from NCNFS → TiOx → CuNi, thereby reducing the d-band center of Cu and Ni, which is beneficial to the desorption of intermediate oxide species of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Therefore, CuNi-TiOx/NCNFS delivers a remarkable bifunctional performance with a low OER overpotential of 258 mV at 10 mA cm-2 and an ORR half-wave potential of 0.85  V. When assembled into ZABs, CuNi-TiOx/NCNFS shows a low potential gap of 0.64 V, a higher power density of 149.6 mW cm-2 at 330 mA cm-2, and an outstanding stability for 250 h at 5mA cm-2. This study provides a novel approach by constructing dual-substrate to tune the electronic structure of active metal sites for efficient rechargeable ZABs.

Modulation in work function of CoTe as bifunctional electrocatalyst for rechargeable zinc air battery

The sluggish kinetics and inferior stability of oxygen electrocatalyst in rechargeable zinc air battery (ZAB) hamper its industrialization. In this work, we activate cobalt telluride (CoTe) by introduction of metallic cobalt (Co) to modulate the work function to facilitate the electron transfer from Co to CoTe during oxygen catalysis; additionally, the three-dimensional porous carbon nanosheets (3DPC) are invited to reduce the resistance towards electrolyte/oxygen diffusion. Thereby, Co-CoTe@3DPC only demands 280 mV overpotential to reach 10 mA cm-2 under alkaline oxygen evolution reaction (OER) condition, relatively lower than commercial iridium oxides (IrO2); besides, the operando electrochemical impedance spectroscopy (EIS) indicates a better resistance towards surface reconstruction than Co@3DPC leading to a superior stability. A Pt-like oxygen reduction reaction (ORR) performance, half-wave potential associated with kinetic current density, is achieved for Co-CoTe@3DPC. A maximum power density of 203 mW cm-2 is achieved and sustains for 800 h. Furthermore, the all-solid-state ZAB offers 97 mW cm-2. Theoretical calculation suggests that the incorporation of metallic Co to CoTe maintains the superb ORR activity and promotes the OER catalysis.

MOF-derived low Ru-loaded high entropy alloy as an efficient and durable self-supporting electrode in rechargeable liquid/flexible Zn-air batteries

Exploiting the high-entropy alloy (HEA) electrocatalysts with the synergistic effect of multi-metal components is an effective approach to address the slow kinetics and undesirable stability of the oxygen evolution reaction (OER) in Zn-air batteries (ZABs), but still faces many challenges. In this study, a multimetallic Metal-organic framework (MOF)-derived HEA catalyst was successfully fabricated on carbon fiber as a flexible self-supporting electrode (denoted as CC@FeCoNiMoRu-HEA/C) for high-performance liquid/flexible ZABs using a facile and cost-effective strategy. The three-dimensional (3D) highly open network framework and hierarchical porous structure accelerate the mass transport of OH-/O2 and charge transfer. The electronic structure adjustment, lattice defects and high entropy effects enable the CC@FeCoNiMoRu-HEA/C catalysts to perform high OER catalytic activity and strong durability while reducing the Ru content and lowering the economic cost. In situ Raman spectra and XPS results reveal the generation of metal-OOH intermediates on the HEA surface during the OER process. In a practical demonstration, the liquid ZAB assembled with CC@FeCoNiMoRu-HEA/C + Pt/C as the air electrode offers stable open-circuit voltage, large power density, excellent specific capacity and satisfactory cycle life, outperforming the commercial RuO2 + Pt/C-based reference ZAB. More attractively, the flexible solid-state ZAB also achieves fast dynamic response, high peak power density, robust cycling stability as well as favorable mechanical flexibility, indicating a promising application prospect in future flexible electronics and wearable devices. This work provides a viable pathway to develop low precious metal-loaded HEAs as advanced OER self-supporting electrocatalysts and realize high-performance flexible energy storage devices.

Co-CoSe heterogeneous fibers with strong interfacial built-in electric field as bifunctional electrocatalyst for high-performance Zn-air battery

The explorations of efficient electrocatalysts to accelerate oxygen reactions in a wide temperature range is a crucial issue to the development of zinc-air batteries (ZAB) for all-climate applications. Herein, the Co-CoSe heterogeneous furry fibers (Co-CoSe@NHF) are developed as a bifunctional oxygen electrocatalyst for ZAB towards wide-temperature range applications. The Co-CoSe heterostructure with large work function difference (ΔWF) endows interfacial electron redistribution, which builds strong interfacial built-in electric field (BIEF) and improves the oxygen reactions. Meanwhile, the Co-CoSe heterostructure is encapsulated by in-situ grown carbon nanotubes, and forms the hollow fiber (NHF) with furry surface and beads-on-string configuration. The highly porous and conductive NHF configuration facilitates the fast kinetics and favors to accommodates volume change during cycling. As a result, the Co-CoSe@NHF achieves the superior bifunctional properties and good reliability for oxygen reactions. Integrated with the Co-CoSe@NHF fiber, the ZAB cell delivers the superior power density (301 mW cm-2) and long-term cycling stability over 280 h at 25 °C, and maintains the power densities of 126 mW cm-2 even the temperature decreases to -25 °C. Moreover, the solid-state ZAB exhibits significant flexibility and superior properties in a wide temperature range. Therefore, this work not only proposes a new strategy to design the high-performance bifunctional electrocatalysts, but also propels the development of flexible power sources for all-climate applications.

Synergistic engineering of heterostructure and oxygen vacancy in cobalt hydroxide/aluminum oxyhydroxide as bifunctional electrocatalysts for urea-assisted hydrogen production

Designing inexpensive, high-efficiency and durable bifunctional catalysts for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) is an encouraging tactic to produce hydrogen with reduced energy expenditure. Herein, oxygen vacancy-rich cobalt hydroxide/aluminum oxyhydroxide heterostructure on nickel foam (denoted as Co(OH)2/AlOOH/NF-100) has been fabricated using one step hydrothermal process. Theoretical calculation and experimental results indicate the electrons transfer from Co(OH)2 to highly active AlOOH results in the interfacial charge redistribution and optimization of electronic structure. Abundant oxygen vacancies in the heterostructure could improve the conductivity and simultaneously serve as the active sites for catalytic reaction. Consequently, the optimal Co(OH)2/AlOOH/NF-100 demonstrates excellent electrocatalytic performance for HER (62.9 mV@10 mA cm-2) and UOR (1.36 V@10 mA cm-2) due to the synergy between heterointerface and oxygen vacancies. Additionally, the in situ electrochemical impedance spectrum (EIS) for UOR suggests that the heterostructured catalyst exhibits rapid reaction kinetics, mass transfer and current response. Importantly, the urea-assisted electrolysis composed of the Co(OH)2/AlOOH/NF-100 manifests a low cell voltage (1.48 V @ 10 mA cm-2) in 1 M KOH containing 0.5 M urea. This work presents a promising avenue to the development of HER/UOR bifunctional electrocatalysts.

Robust bifunctionality in an oxygen electrode via core-shell heterostructure construction

A Co-CoSe core-shell heterostructure encapsulated into nitrogen-doped carbon nanotubes enables superior zinc air battery performance (172 mW cm-2) and stability (970 h). The enhanced bifunctionality and stability originates from the modulated d band center and confinement effect, respectively.

Theoretical Study on the O-H Fracture of Methanol on PtnCu4-n (n = 1, 2, 3) Catalysts with Different Coverages

Direct methanol fuel cells (DMFCs) have attracted increasing attention as a very promising and important energy source. In this paper, density functional theory (DFT) is used to study the structure and O-H fracture mechanism of methanol adsorption on PtnCu4-n (111) (n = 1, 2, 3) binary metal catalyst surfaces under different coverages. By comparing the adsorption energy and dehydrogenation energy barriers of methanol, it is found that the adsorption strength and dehydrogenation energy barriers of methanol on Pt and Cu sites decreased with increasing coverage. At the same Pt and Cu ratio, methanol is more easily adsorbed on Cu sites. When Pt/Cu = 3:1 and 1:3, the PtCu binary catalyst has a significant impact on the energy barrier of breaking the O-H bond in methanol with the increase of coverage. Especially when Pt/Cu = 1:3 and the coverage is 1/4 ML, the energy barriers of O-H bond breaking in methanol on Pt and Cu sites are 0.63 and 0.61 eV, respectively, which are lower than that on pure Pt. It means that the Cu sites played a very important role in reducing the O-H fracture energy barrier of methanol. When Pt/Cu = 1:1, the change in the dehydrogenation energy barrier of methanol on Pt sites and Cu sites is not significant, indicating that the coverage has little effect on it.

Cation vacancy modulated Cu3P-CoP heterostructure electrocatalyst for boosting hydrogen evolution at high current densities and coupling Zn-H2O battery

Exploiting highly efficient, cost-effective and stable electrocatalysts is key to decreasing hydrogen evolution reaction (HER) kinetics energy barrier. Herein, the alkaline HER kinetics energy barrier can greatly reduce by the joint strategies of the cation vacancy and heterostructure engineering, which is seldom explored and remains ambiguous. In this study, an efficient and stable copper foam-supported Cu3P-CoP heterostructure electrocatalyst with cation vacancy defects (defined as Cu3P-CoP-VAl/CF) was designed for HER via the successive coprecipitation, electrodeposition, alkali etching and phosphorization treatments. As anticipated, the as-obtained Cu3P-CoP-VAl/CF electrocatalyst reveals a remarkable catalytic activity for HER with a low overpotential of 205 mV at a current density of 100 mA·cm-2, a high turnover frequency value of 1.05 s-1 at an overpotential of 200 mV and a small apparent activation energy (Ea) of 9 kJ·mol-1, while shows superior long-term stability at large current densities of 100 and 240 mA·cm-2. Systematic experiment and characterization data demonstrate that the formed cation vacancy could optimize the Ea, leading to the decrease of the kinetic barriers of Cu3P-CoP/CF heterostructure, as well as the established heterogeneous interface induced a synergistic effect between biphasic components on boosting the kinetics toward HER. The results of density functional theory disclose that the synergistic effect of Cu3P-CoP heterostructure could decrease the energy barrier and optimize Gibbs free energy of hydrogen adsorption, resulting in the enhancement of intrinsic catalytic activity of Cu3P-CoP-VAl/CF. More significantly, the alkali-cell assembled by Cu3P-CoP-VAl/CF (cathode) and RuO2/CF (anode) behaves outstanding water splitting performance, delivering a current density of 10 mA·cm-2 at a relatively small applied voltage of 1.58 V, along with encouraging long-term durability. In addition, the alkaline Zn-H2O battery with Cu3P-CoP-VAl/CF as the cathode has been fabricated for the simultaneous generation of electricity and hydrogen, which displays a large power density of up to 4.1 mW·cm-2. The work demonstrates that rational strategy for the design of competent electrocatalysts can effectively accelerate the kinetics of HER, which supplies valuable insights for practical applications in overall water splitting.

A superior zinc-air battery performance achieved by CoO/Fe3O4 heterostructured nanosheets

CoO/Fe3O4 nanosheets exhibit a superior rechargeable zinc-air battery (ZAB) performance of 276 mW cm-2 and stability over 600 h. The all-solid-state ZAB also affords a high power density of 107 mW cm-2.

Tip and heterogeneous effects co-contribute to a boosted performance and stability in zinc air battery

The zinc-air battery (ZAB) performance and stability strongly depend on the structure of bifunctional electrocatalyst for oxygen reduction/evolution reaction (ORR/OER). In this work, we combine the tip and heterogeneous effects to construct cobalt/cobalt oxide heterostructure nanoarrays (Co/CoO-NAs). Due to the formed heterostructure, more oxygen vacancies are found for Co/CoO-NAs resulting in a 1.4-fold higher ORR intrinsic activity than commercial carbon supported platinum electrocatalyst (Pt/C) at 0.8 V versus reversible hydrogen electrode (vs. RHE). Moreover, a fast surface reconstruction is observed for Co/CoO-NAs during OER catalysis evidenced by in-situ electrochemical impedance spectroscopy and Raman tests. In addition, the tip effect efficiently lowers the mass transfer resistance triggering a low overpotential of 347 mV at 200 mA cm-2 for Co/CoO-NAs. The strong electronic interplay between cobalt (Co) and cobalt oxide (CoO) contributes to a stable battery performance during 1200 h galvanostatic charge-discharge test at 5 mA cm-2. This work offers a new avenue to construct high-performance and stable oxygen electrocatalyst for rechargeable ZAB.

Synergistic vacancy engineering of Co/MnO@NC catalyst for superior oxygen reduction reaction in liquid/solid zinc-air batteries

The pursuit of efficient and economically viable catalysts for liquid/solid-state zinc-air batteries (ZABs) is of paramount importance yet presents formidable challenge. Herein, we synthesized a vacancy-rich cobalt/manganese oxide catalyst (Co/MnO@NC) stabilized on a nitrogen-doped mesoporous carbon (NC) nanosphere matrix by leveraging hydrothermal and high-temperature pyrolysis strategy. The optimized Co/MnO@NC demonstrates fast reaction kinetics and large limiting current densities comparable to commercial Pt/C in alkaline electrolyte for oxygen reduction reaction (ORR). Moreover, the Co/MnO@NC serves as an incredible cathode material for both liquid and flexible solid-state ZABs, delivering impressive peak power densities of 217.7 and 63.3 mW cm-2 and robust long-term stability (459 h), outperforming the state-of-the-art Pt/C and majority of the currently reported catalysts. Research indicates that the superior performance of the Co/MnO@NC catalyst primarily stems from the synergy between the heightened electrical conductivity of metallic Co and the regulatory capacity of MnO on adsorbed oxygen intermediates. In addition, the abundance of vacancies regulates the electronic configuration, and superhydrophilicity facilitates efficient electrolyte diffusion, thereby effectively ensuring optimal contact between the active site and reactants. Besides, the coexisting NC layer avoids the shedding of active sites, resulting in high stability. This work provides a viable approach for designing and advancing high-performance liquid/solid-state ZABs, highlighting the great potential of energy storage technology.

Identifying the Active Sites in MoSi2@MoO3 Heterojunctions for Enhanced Hydrogen Evolution

Developing Two-dimensional (2D) Mo-based heterogeneous nanomaterials is of great significance for energy conversion, especially in alkaline hydrogen evolution reaction (HER), however, it remains a challenge to identify the active sites at the interface due to the structure complexity. Herein, the real active sites are systematically explored during the HER process in varied Mo-based 2D materials by theoretical computational and magnetron sputtering approaches first to filtrate the candidates, then successfully combined the MoSi2 and MoO3 together through Oxygen doping to construct heterojunctions. Benefiting from the synergistic effects between the MoSi2 and MoO3, the obtained MoSi2@MoO3 exhibits an unprecedented overpotential of 72 mV at a current density of 10 mA cm-2. Density functional theory calculations uncover the different Gibbs free energy of hydrogen adsorption (ΔGH*) values achieved at the interfaces with different sites as adsorption sites. The results can facilitate the optimization of heterojunction electrocatalyst design principles for the Mo-based 2D materials.