NiCoFe Layered Triple Hydroxides with Porous Structures as High-Performance Electrocatalysts for Overall Water Splitting

We report a type of NiCoFe layered triple hydroxides (LTHs) supported on carbon fiber cloth (CFC) (NiCoFe LTHs/CFC) as high-performance electrocatalysts for overall water splitting in alkaline media. The NiCoFe LTHs/CFC as an oxygen evolution reaction (OER) electrocatalyst shows excellent catalytic activity and durability, such as low overpotential of ∼239 mV at 10 mA cm^–2, small Tafel slope of ∼32 mV dec^–1 and conservation rate of catalytic activity (∼99%) after 12 h of continuous electrolysis at 20 mA cm^–2. As a hydrogen evolution reaction (HER) electrocatalyst, NiCoFe LTHs/CFC also shows low onset potential, small Tafel slope, and superior durability. The NiCoFe LTHs/CFC-based overall water splitting exhibits a low onset potential (∼1.51 V), a low splitting potential (∼1.55 V) at 10 mA cm^–2, and excellent durability, and the performance is comparable to that of IrO₂/Pt-based overall water splitting. This work will open a new avenue toward the development of high-performance and inexpensive layered triple hydroxides electrocatalysts

Enhanced Catalytic Activity and Stability of Pt/CeO₂/PANI Hybrid Hollow Nanorod Arrays for Methanol Electro-oxidation

Here, we designed and fabricated novel Pt/CeO₂/PANI three-layered hollow nanorod arrays (THNRAs) as advanced electrocatalysts for methanol oxidation by combining the merits of CeO₂, PANI, multilayered structure, and hollow nanorod arrays. The synthesized Pt/CeO₂/PANI THNRAs exhibit higher electrocatalytic activity and better stability toward the oxidation of methanol than Pt/PANI HNRAs, Pt/CeO₂ HNRAs, and commercial Pt/C catalysts. The enhanced electrocatalytic performance of the Pt/CeO₂/PANI THNRAs may be due to the synergistic effects among Pt, CeO₂, and PANI and the special three-layered hollow nanorod arrays, which can provide short diffusion paths for electroactive species and high-availability of electrocatalysts. The facile synthesis method can be considered as a promising strategy to design low-cost, high-performance electrocatalysts for fuel cells

Cu₂O–Cu Hybrid Foams as High-Performance Electrocatalysts for Oxygen Evolution Reaction in Alkaline Media

Here 3D Cu₂O–Cu hybrid foams are developed as high-performance electrocatalysts for OER in alkaline solution. The hybrid foams are composed of Cu₂O–Cu dendrites with high surface area and high-speed electronic transmission networks, and they can provide fast transportation and short diffusion path for electrolyte and evolved O₂ bubbles. As the special surface and structure effects, the Cu₂O–Cu hybrid foams exhibit low onset overpotential of ∼250 mV, small Tafel slope of 67.52 mV dec^–1, and high durability over 50 h at a current density of 10 mA cm^–2 for OER in alkaline solution. The results of this study may be particularly beneficial for the development of a type of hybrid porous foam electrocatalysts for the electrochemical process in which at least one gas-phase is involved, such as H₂ or O₂ evolution reaction and O₂ or CO₂ electroreduction reaction

Pt-like Hydrogen Evolution Electrocatalysis on PANI/CoP Hybrid Nanowires by Weakening the Shackles of Hydrogen Ions on the Surfaces of Catalysts

The search for high active, stable, and cost-efficient hydrogen evolution reaction (HER) electrocatalysts for water electrolysis has attracted great interest. The coordinated water molecules in the hydronium ions will obviously reduce the positive charge density of H⁺ and hamper the ability of H⁺ to receive electrons from the cathode, leading to large overpotential of HER on nonprecious metal catalysts. Here we realize Pt-like hydrogen evolution electrocatalysis on polyaniline (PANI) nanodots (NDs)-decorated CoP hybrid nanowires (HNWs) supported on carbon fibers (CFs) (PANI/CoP HNWs-CFs) as PANI can effectively capture H⁺ from hydronium ions to form protonated amine groups that have higher positive charge density than those of hydronium ions and can be electro-reduced easily. The PANI/CoP HNWs-CFs as low-cost electrocatalysts show excellent catalytic performance toward HER in acidic solution, such as super high catalytic activity, small Tafel slope, and superior stability

In Situ Derived Ni_<i>x</i>Fe_1–<i>x</i>OOH/NiFe/Ni_<i>x</i>Fe_1–<i>x</i>OOH Nanotube Arrays from NiFe Alloys as Efficient Electrocatalysts for Oxygen Evolution

Herein, Ni_<i>x</i>Fe_1–<i>x</i>OOH/NiFe/Ni_<i>x</i>Fe_1–<i>x</i>OOH sandwich-structured nanotube arrays (SNTAs) supported on carbon fiber cloth (CFC) (Ni_<i>x</i>Fe_1–<i>x</i>OOH/NiFe/Ni_<i>x</i>Fe_1–<i>x</i>OOH SNTAs–CFC) have been developed as flexible high-performance oxygen evolution reaction (OER) catalysts by a facile in situ electrochemical oxidation of NiFe metallic alloy nanotube arrays during oxygen evolution process. Benefiting from the advantages of high conductivity, hollow nanotube array, and porous structure, Ni_<i>x</i>Fe_1–<i>x</i>OOH/NiFe/Ni_<i>x</i>Fe_1–<i>x</i>OOH SNTAs–CFC exhibited a low overpotential of ∼220 mV at the current density of 10 mA cm^–2 and a small Tafel slope of 57 mV dec^–1 in alkaline solution, both of which are smaller than those of most OER electrocatalysts. Furthermore, Ni_<i>x</i>Fe_1–<i>x</i>OOH/NiFe/Ni_<i>x</i>Fe_1–<i>x</i>OOH SNTAs–CFC exhibits excellent stability at 100 mA cm^–2 for more than 30 h. It is believed that the present work can provide a valuable route for the design and synthesis of inexpensive and efficient OER electrocatalysts

Design and Synthesis of MnO₂/Mn/MnO₂ Sandwich-Structured Nanotube Arrays with High Supercapacitive Performance for Electrochemical Energy Storage

We demonstrate the design and fabrication of novel nanoarchitectures of MnO₂/Mn/MnO₂ sandwich-like nanotube arrays for supercapacitors. The crystalline metal Mn layers in the MnO₂/Mn/MnO₂ sandwich-like nanotubes uniquely serve as highly conductive cores to support the redox active two-double MnO₂ shells with a highly electrolytic accessible surface area and provide reliable electrical connections to MnO₂ shells. The maximum specific capacitances of 937 F/g at a scan rate of 5 mV/s by cyclic voltammetry (CV) and 955 F/g at a current density of 1.5 A/g by chronopotentiometry were achieved for the MnO₂/Mn/MnO₂ sandwich-like nanotube arrays in solution of 1.0 M Na₂SO₄. The hybrid MnO₂/Mn/MnO₂ sandwich-like nanotube arrays exhibited an excellent rate capability with a high specific energy of 45 Wh/kg and specific power of 23 kW/kg and excellent long-term cycling stability (less 5% loss of the maximum specific capacitance after 3000 cycles). The high specific capacitance and charge–discharge rates offered by such MnO₂/Mn/MnO₂ sandwich-like nanotube arrays make them promising candidates for supercapacitor electrodes, combining high-energy densities with high levels of power delivery

α‑Fe₂O₃@PANI Core–Shell Nanowire Arrays as Negative Electrodes for Asymmetric Supercapacitors

Highly ordered three-dimensional α-Fe₂O₃@PANI core–shell nanowire arrays with enhanced specific areal capacity and rate performance are fabricated by a simple and cost-effective electrodeposition method. The α-Fe₂O₃@PANI core–shell nanowire arrays provide a large reaction surface area, fast ion and electron transfer, and good structure stability, which all are beneficial for improving the electrochemical performance. Here, high-performance asymmetric supercapacitors (ASCs) are designed using α-Fe₂O₃@PANI core–shell nanowire arrays as anode and PANI nanorods grown on carbon cloth as cathode, and they display a high volumetric capacitance of 2.02 mF/cm³ based on the volume of device, a high energy density of 0.35 mWh/cm³ at a power density of 120.51 mW/cm³, and very good cycling stability with capacitance retention of 95.77% after 10 000 cycles. These findings will promote the application of α-Fe₂O₃@PANI core–shell nanowire arrays as advanced negative electrodes for ASCs

Asymmetric Paper Supercapacitor Based on Amorphous Porous Mn₃O₄ Negative Electrode and Ni(OH)₂ Positive Electrode: A Novel and High-Performance Flexible Electrochemical Energy Storage Device

Here we synthesize novel asymmetric all-solid-state paper supercapacitors (APSCs) based on amorphous porous Mn₃O₄ grown on conducting paper (NGP) (Mn₃O₄/NGP) negative electrode and Ni­(OH)₂ grown on NGP (Ni­(OH)₂/NGP) as positive electrode, and they have attracted intensive research interest owing to their outstanding properties such as being flexible, ultrathin, and lightweight. The fabricated APSCs exhibit a high areal <i>C</i>_sp of 3.05 F/cm³ and superior cycling stability. The novel asymmetric APSCs also exhibit high energy density of 0.35 mW h/cm³, high power density of 32.5 mW/cm³, and superior cycling performance (<17% capacitance loss after 12 000 cycles at a high scan rate of 100 mV/s). This work shows the first example of amorphous porous metal oxide/NGP electrodes for the asymmetric APSCs, and these systems hold great potential for future flexible electronic devices

Fe-Doped Ni₂P/NiSe₂ Composite Catalysts for Urea Oxidation Reaction (UOR) for Energy-Saving Hydrogen Production by UOR-Assisted Water Splitting

The development of efficient urea oxidation reaction (UOR) catalysts helps UOR replace the oxygen evolution reaction (OER) in hydrogen production from water electrolysis. Here, we prepared Fe-doped Ni2P/NiSe2 composite catalyst (Fe–Ni2P/NiSe2-12) by using phosphating-selenizating and acid etching to increase the intrinsic activity and active areas. Spectral characterization and theoretical calculations demonstrated that electrons flowed through the Ni–P–Fe–interface–Ni–Se–Fe, thus conferring high UOR activity to Fe–Ni2P/NiSe2-12, which only needed 1.39 V vs RHE to produce the current density of 100 mA cm–2. Remarkably, this potential was 164 mV lower than that required for the OER under the same conditions. Furthermore, EIS demonstrated that UOR driven by the Fe–Ni2P/NiSe2-12 exhibited faster interfacial reactions, charge transfer, and current response compared to OER. Consequently, the Fe–Ni2P/NiSe2-12 catalyst can effectively prevent competition with OER and NSOR, making it suitable for efficient hydrogen production in UOR-assisted water electrolysis. Notably, when water electrolysis is operated at a current density of 40 mA cm–2, this UOR-assisted system can achieve a decrease of 140 mV in the potential compared to traditional water electrolysis. This study presents a novel strategy for UOR-assisted water splitting for energy-saving hydrogen production

Design of Pd/PANI/Pd Sandwich-Structured Nanotube Array Catalysts with Special Shape Effects and Synergistic Effects for Ethanol Electrooxidation

Low cost, high activity, and long-term durability are the main requirements for commercializing fuel cell electrocatalysts. Despite tremendous efforts, developing non-Pt anode electrocatalysts with high activity and long-term durability at low cost remains a significant technical challenge. Here we report a new type of hybrid Pd/PANI/Pd sandwich-structured nanotube array (SNTA) to exploit shape effects and synergistic effects of Pd-PANI composites for the oxidation of small organic molecules for direct alcohol fuel cells. These synthesized Pd/PANI/Pd SNTAs exhibit significantly improved electrocatalytic activity and durability compared with Pd NTAs and commercial Pd/C catalysts. The unique SNTAs provide fast transport and short diffusion paths for electroactive species and high utilization rate of catalysts. Besides the merits of nanotube arrays, the improved electrocatalytic activity and durability are especially attributed to the special Pd/PANI/Pd sandwich-like nanostructures, which results in electron delocalization between Pd d orbitals and PANI π-conjugated ligands and in electron transfer from Pd to PANI