Acid Treated Carbon as Anodic Electrocatalysts toward Direct Ascorbic Acid Alkaline Membrane Fuel Cells; [酸处理的碳作为阳极电催化剂用于直接抗坏血酸碱性膜燃料电池]北大核心CSCD

In order to improve the hydrophilicity and electrocatalytic activity, commercial carbon black (BP 2000) was subjected to acid treatment to obtain acid-treated carbon (ATC).The generation of rich oxygen-containing groups on the surface of the ATC was proved by X-ray photoelectron spectra (XPS), Fourier transform-infra red spectra (FTIR), thermogravimetric analysis (TG) and contact angle measurement.UV-vis spectra were firstly recorded to calculate activation energy (Ea) of ascorbic acid (AA) chemical oxidation in alkaline conditions by oxygen in air and the Ea value was determined to be 37.1 kJ·mol-1.Additionally, electrochemical impedance spectra (EIS) were used to evaluate unprecedented Eaelectrochem of ATC as electrocatalysts toward ascorbic acid (AA) oxidation in alkaline media.The Eaelectrochem values of electrochemical oxidation in alkaline membrane electrode assembly (MEA) setup of a single cell without and with ATC as the anodic electrocatalysts were calculated to be 34.5 and 26.5 kJ·mol-1, respectively.The diminished Eaelectrochem suggests that ATC does function as an effective anodic electrocatalyst.Furthermore, the ATC was applied in direct ascorbic acid alkaline membrane fuel cell (DAAFC) for the first time.We optimized a series of parameters for the fabrication of MEAs including catalyst coated membrane (CCM) or catalyst coated gas diffusion layer membrane (CDM), loading of anodic electrocatalyst, and ionomer content in the electrocatalyst slurry.It turned out that the CCM with the ATC loading of 0.5 mg·cm-2 and 25wt% ionomer reached a high power density of 18.5 mW·cm-2, which is higher than that of using PtRu/C as anodic electrocatalyst (less than 5.0 mW·cm-2).In addition, the DAAFC fed with 15 mL·min-1 of the fuel containing 0.5 mol·L-1 AA and 1 mol·L-1 NaOH aq.could stably hold a power density at 4 mW·cm-2 for 25 min. © 2018 Journal of Electrochemistry. All rights reserved.     

Methanol oxidation in acidic and alkaline electrolytes using PtRuIn/C electrocatalysts prepared by borohydride reduction process

PtRuIn/C electrocatalysts( 20% metal loading by weight) were prepared by sodium borohydride reduction process using H_2PtCl6·6H_2O,RuCl_3·xH_2O and InCl_3·xH_2O as metal sources,borohydride as reducing agent and Carbon Vulcan XC72 as support. The synthetized PtRuIn/C electrocatalysts were characterized by X-ray diffraction( XRD),energy dispersive analysis( EDX),transmission electron microscopy( TEM),cyclic voltammetry( CV),chronoamperommetry( CA) and polarization curves in alkaline and acidic electrolytes( single cell experiments). The XRD patterns showPtpeaks are attributed to the face-centered cubic( fcc) structure,and a shift of Pt( fcc) peaks indicates that Ru or In is incorporated into Ptlattice. TEMmicrographs showmetal nanoparticles with an average nanoparticle size between 2.7 and 3.5 nm. Methanol oxidation in acidic and alkaline electrolytes was investigated at room temperature,by CV and CA. PtRu/C( 50 ∶ 50) shows the highest activity among all electrocatalysts in study considering methanol oxidation for acidic and alkaline electrolyte. Polarization curves at 80 ℃ showPtRuIn/C( 50 ∶ 25 ∶ 25)with superior performance for methanol oxidation,when compared to Pt/C,PtIn/C and PtRu/C for both electrolytes. The best performance obtained by PtRuIn/C( 50 ∶ 25 ∶ 25) in real conditions could be associated with the increased kinetics reaction and/or with the occurrence simultaneously of the bifunctional mechanism and electronic effect resulting from the presence of Ptalloy.     

Controllable Synthesis of Few‐Layer Bismuth Subcarbonate by Electrochemical Exfoliation for Enhanced CO2 Reduction Performance

Two‐dimensional (2D) engineering of materials has been recently explored to enhance the performance of electrocatalysts by reducing their dimensionality and introducing more catalytically active ones. In this work, controllable synthesis of few‐layer bismuth subcarbonate nanosheets has been achieved via an electrochemical exfoliation method. These nanosheets catalyse CO₂ reduction to formate with high faradaic efficiency and high current density at a low overpotential owing to the 2D structure and co‐existence of bismuth subcarbonate and bismuth metal under catalytic turnover conditions. Two underlying fast electron transfer processes revealed by Fourier‐transformed alternating current voltammetry (FTacV) are attributed to CO₂ reduction at bismuth subcarbonate and bismuth metal. FTacV results also suggest that protonation of CO₂^.? is the rate determining step for bismuth catalysed CO₂ reduction.     

Engineering an Earth‐Abundant Element‐Based Bifunctional Electrocatalyst for Highly Efficient and Durable Overall Water Splitting

The simultaneous and efficient evolution of hydrogen and oxygen with earth‐abundant, highly active, and robust bifunctional electrocatalysts is a significant concern in water splitting. Herein, non‐noble metal‐based Ni–Co–S bifunctional catalysts with tunable stoichiometry and morphology are realized. The engineering of electronic structure and subsequent morphological design synergistically contributes to significantly elevated electrocatalytic performance. Stable overpotentials (η₁₀) of 243 mV (vs reversible hydrogen electrode) for oxygen evolution reaction (OER) and 80 mV for hydrogen evolution reaction (HER), as well as Tafel slopes of 54.9 mV dec^?1 for OER and 58.5 mV dec^?1 for HER, are demonstrated. In addition, density functional theory calculations are performed to determine the optimal electronic structure via the electron density differences to verify the enhanced OER activity is related to the Co top site on the (110) surface. Moreover, the tandem bifunctional NiCo₂S₄ exhibit a required voltage of 1.58 V (J = 10 mA cm^?2) for simultaneous OER and HER, and no obvious performance decay is observed after 72 h. When integrated with a GaAs solar cell, the resulting photoassisted water splitting electrolyzer shows a certified solar‐to‐hydrogen efficiency of up to 18.01%, further demonstrating the feasibility of engineering protocols and the promising potential of bifunctional NiCo₂S₄ for large‐scale overall water splitting.     

Targeted Synergy between Adjacent Co Atoms on Graphene Oxide as an Efficient New Electrocatalyst for Li–CO2 Batteries

Li–CO₂ batteries are an attractive technology for converting CO₂ into energy. However, the decomposition of insulating Li₂CO₃ on the cathode during discharge is a barrier to practical application. Here, it is demonstrated that a high loading of single Co atoms (≈5.3%) anchored on graphene oxide (adjacent Co/GO) acts as an efficient and durable electrocatalyst for Li–CO₂ batteries. This targeted dispersion of atomic Co provides catalytically adjacent active sites to decompose Li₂CO₃. The adjacent Co/GO exhibits a highly significant sustained discharge capacity of 17 358 mA h g^?1 at 100 mA g^?1 for >100 cycles. Density functional theory simulations confirm that the adjacent Co electrocatalyst possesses the best performance toward the decomposition of Li₂CO₃ and maintains metallic‐like nature after the adsorption of Li₂CO₃.     

Constructing Conductive Interfaces between Nickel Oxide Nanocrystals and Polymer Carbon Nitride for Efficient Electrocatalytic Oxygen Evolution Reaction

Combining transition metal oxide catalysts with conductive carbonaceous material is a feasible way to improve the conductivity. However, the electrocatalytic performance is usually not distinctly improved because the interfacial resistance between metal oxides and carbon is still large and thereby hinders the charge transport in catalysis. Herein, the conductive interface between poorly conductive NiO nanoparticles and semi‐conductive carbon nitride (CN) is constructed. The NiO/CN exhibits much‐enhanced oxygen evolution reaction (OER) performance than corresponding NiO and CN in electrolytes of KOH solution and phosphate buffer saline, which is also remarkably superior over NiO/C, commercial RuO₂, and mostly reported NiO‐based catalysts. X‐ray photoelectron spectroscopy and extended X‐ray absorption fine structure spectrum reveal that a metallic Ni–N bond is formed between NiO and CN. Density functional theory calculations suggest that NiO and CN linked by a Ni–N bond possess a low Gibbs energy for OER intermediate adsorptions, which not only improves the transfer of charge but also promotes the transmission of mass in OER. The metal–nitrogen bonded conductive and highly active interface pervasively exists between CN and other transition metal oxides including Co₃O₄, CuO, and Fe₂O₃, making it promising as an inexpensive catalyst for efficient water splitting.     

One‐Pot Synthesis of Framework Porphyrin Materials and Their Applications in Bifunctional Oxygen Electrocatalysis

Organic framework materials constructed by covalently linking organic building blocks into framework structures are highly regarded as paragons to precisely control the material structure at the atomic level. Herein, a direct synthesis methodology is proposed as a guidance for the bulk synthesis of organic framework materials. Framework porphyrin (POF) materials are one‐pot synthesized to demonstrate the advances of the direct synthesis methodology. The as‐synthesized POF materials are intrinsically 2D and exhibit impressive versatility in composition, structure, morphology, and function, delivering a free‐standing POF film, hybrids of POF and nanocarbon, and cobalt‐coordinated POF. When applied as electrocatalysts for oxygen reduction reaction and oxygen evolution reaction, the cobalt‐coordinated POF exhibits excellent bifunctional electrocatalytic performances comparable with noble‐metal‐based electrocatalysts. The direct synthesis methodology and resultant POF materials demonstrate the ability of controlling materials at the atomic level for energy electrocatalysis.     

2D Nitrogen‐Doped Carbon Nanotubes/Graphene Hybrid as Bifunctional Oxygen Electrocatalyst for Long‐Life Rechargeable Zn–Air Batteries

The rational construction of efficient bifunctional oxygen electrocatalysts is of immense significance yet challenging for rechargeable metal–air batteries. Herein, this work reports a metal–organic framework derived 2D nitrogen‐doped carbon nanotubes/graphene hybrid as the efficient bifunctional oxygen electrocatalyst for rechargeable zinc–air batteries. The as‐obtained hybrid exhibits excellent catalytic activity and durability for the oxygen electrochemical reactions due to the synergistic effect by the hierarchical structure and heteroatom doping. The assembled rechargeable zinc–air battery achieves a high power density of 253 mW cm^?2 and specific capacity of 801 mAh g_Zn^?1 with excellent cycle stability of over 3000 h at 5 mA cm^?2. Moreover, the flexible solid‐state rechargeable zinc–air batteries assembled by this hybrid oxygen electrocatalyst exhibits a high discharge power density of 223 mW cm^?2, which can power 45 light‐emitting diodes and charge a cellphone. This work provides valuable insights in designing efficient bifunctional oxygen electrocatalysts for long‐life metal–air batteries and related energy conversion technologies.     

Efficient Optimization of Electron/Oxygen Pathway by Constructing Ceria/Hydroxide Interface for Highly Active Oxygen Evolution Reaction

Owing to the unique electronic properties, rare‐earth modulations in noble‐metal electrocatalysts emerge as a critical strategy for a broad range of renewable energy solutions such as water‐splitting and metal–air batteries. Beyond the typical doping strategy that suffers from synthesis difficulties and concentration limitations, the innovative introduction of rare‐earth is highly desired. Herein, a novel synthesis strategy is presented by introducing CeO₂ support for the nickel–iron–chromium hydroxide (NFC) to boost the oxygen evolution reaction (OER) performance, which achieves an ultralow overpotential at 10 mA cm^?2 of 230.8 mV, the Tafel slope of 32.7 mV dec^?1, as well as the excellent durability in alkaline solution. Density functional theory calculations prove the established d–f electronic ladders, by the interaction between NFC and CeO₂, evidently boosts the high‐speed electron transfer. Meanwhile, the stable valence state in CeO₂ preserves the high electronic reactivity for OER. This work demonstrates a promising approach in fabricating a nonprecious OER electrocatalyst with the facilitation of rare‐earth oxides to reach both excellent activity and high stability.