高活性、低载量的PtCo/C质子交换膜燃料电池催化剂的合成

利用逐步合成的方法,合成了一系列不同量硝酸处理的PtCo/C催化剂。通过燃料电池测试装置对催化剂进行了测试,结果表明PtCo/C催化剂在较低载量情况下,有着很好的性能：在50 kPa背压下,0.9 V下的电流密度达到44 mA·cm^-2,0.8 V下的电流密度超过300 mA·cm^-2;200 kPa背压下,最高功率密度超过1 300 mW·cm^-2。通过X射线衍射（XRD）、透射电子显微镜（TEM）对合成的PtCo/C催化剂的形貌、组成进行了表征。XRD结果表明,催化剂中,Pt以Pt₃Co和Pt颗粒形式存在。燃料电池测试结果表明,这一系列的催化剂中,经2 mL质量分数65%的浓硝酸配制的水溶液处理过的PtCo/C催化剂,具有最好的燃料电池性能以及良好的稳定性。     

Tungsten‐Doped L10‐PtCo Ultrasmall Nanoparticles as a High‐Performance Fuel Cell Cathode

The commercialization of proton exchange membrane fuel cells (PEMFCs) relies on highly active and stable electrocatalysts for oxygen reduction reaction (ORR) in acid media. The most successful catalysts for this reaction are nanostructured Pt‐alloy with a Pt‐skin. The synthesis of ultrasmall and ordered L1₀‐PtCo nanoparticle ORR catalysts further doped with a few percent of metals (W, Ga, Zn) is reported. Compared to commercial Pt/C catalyst, the L1₀‐W‐PtCo/C catalyst shows significant improvement in both initial activity and high‐temperature stability. The L1₀‐W‐PtCo/C catalyst achieves high activity and stability in the PEMFC after 50 000 voltage cycles at 80 °C, which is superior to the DOE 2020 targets. EXAFS analysis and density functional theory calculations reveal that W doping not only stabilizes the ordered intermetallic structure, but also tunes the Pt‐Pt distances in such a way to optimize the binding energy between Pt and O intermediates on the surface.     

Cobalt Phenanthroline–Indole Macrocycles as Highly Active Electrocatalysts for Oxygen Reduction

The replacement of scarce and expensive platinum species poses a challenge in fuel‐cell development. The design and synthesis of a novel type of Co^II–N₄ macrocyclic complex, [CoN₄], based on the phenanthroline–indole macrocyclic ligand (PIM) is reported. This unique ligand allows the formation of mono‐ and dinuclear complexes with defined active sites that facilitate the direct four‐electron reduction of oxygen. Electrochemical measurements revealed that the [CoN₄]/C (20 wt %) catalysts have a high activity and long‐term stability for the oxygen‐reduction reaction (ORR) under alkaline conditions, similar to the Pt/C catalyst. These structurally well‐defined complexes represent a nonprecious alternative to platinum species for future fuel‐cell applications.     

Electrochemical characteristics of platinum-based binary catalysts for middle-temperature hydrogen-air fuel cells with phosphoric acid electrolyte

The high-temperature synthesis based on commercial catalyst E-TEK (40% Pt) using cobalt, chromium, and iron organic precursors as well as d-metal salts yielded PtM (1:1) catalysts (PtCo, PtCr, PtMn, PtNi, PtFe, and PtV) for electroreduction of molecular oxygen in concentrated H₃PO₄ at the temperature of 160°C. The phase composition of the synthesized catalysts was studied by powder diffraction. The electrochemical measurements were carried out in 15 M H₃PO₄ at 20 and 160°C using a model gas diffusion electrode. An assumption was made that close charging curves recorded for synthesized PtM catalysts in both hydrogen and oxygen adsorption ranges were due to formation of the core-shell structure: alloy core and surface layers enriched with platinum. The Tafel curves of molecular oxygen reduction in 15 M H₃PO₄ at 160°C were characterized with the sole slope of 0.10 to 0.11 V. The catalytic activity in the range of potentials from 0.8 to 0.9 V (RHE) was shown approximately twice as that of pure platinum catalyst. The highest activity was recorded for PtCo and PtCr binary catalysts. Their use in middle-temperature hydrogen-air fuel cells with solid polymeric electrolyte based on polybenzimidazole doped with phosphoric acid enabled 2- to 3-fold decrease of the platinum share in the cathode.     

A “Pre-Division Metal Clusters” Strategy to Mediate Efficient Dual-Active Sites ORR Catalyst for Ultralong Rechargeable Zn-Air Battery

To conquer the bottleneck of sluggish kinetics in cathodic oxygen reduction reaction (ORR) of metal-air batteries, catalysts with dual-active centers have stood out. Here, a “pre-division metal clusters” strategy is firstly conceived to fabricate a N,S-dual doped honeycomb-like carbon matrix inlaid with CoN₄ sites and wrapped Co₂P nanoclusters as dual-active centers (Co₂P/CoN₄@NSC-500). A crystalline {Co^II ₂ } coordination cluster divided by periphery second organic layers is well-designed to realize delocalized dispersion before calcination. The optimal Co₂P/CoN₄@NSC-500 executes excellent 4e⁻ ORR activity surpassing the benchmark Pt/C. Theoretical calculation results reveal that the CoN₄ sites and Co₂P nanoclusters can synergistically quicken the formation of *OOH on Co sites. The rechargeable Zn-air battery (ZAB) assembled by Co₂P/CoN₄@NSC-500 delivers ultralong cycling stability over 1742 hours (3484 cycles) under 5 mA cm⁻² and can light up a 2.4 V LED bulb for ≈264 hours, evidencing the promising practical application potentials in portable devices.     

Direct ethanol oxidation fuel cell with anionite membrane and alkaline electrolyte

A number of cathode catalysts were synthesized from nitrogen-containing organic complexes on XC-72R carbon black for an alkaline electrolyte. The catalysts were studied by the rotating disc electrode (RDE) technique. The polyacrilonitrile (PAN), phthalocyanine (Pc), and cobalt tetra(methoxyphenyl)porphyrin (CoTMPP) systems showed the highest activity. The slope of the oxygen polarization curves in the first region in 1 M KOH was 35–40 mV; this corresponds to concentration polarization in an alkaline solution in the O₂-HO₂⁻ system. A cyclic voltammetry study demonstrated that the catalytic systems with the highest corrosion stability were Pc + Co + Fe/XC-72R and CoTMPP/XC-72R pyropolymer. The activity of the catalysts decreased by 20–25% compared with the initial current densities on average. An ethanol-oxygen fuel cell with a Fumasep FAA anionite membrane and nonplatinum catalysts was tested. The maximum power density was 32 mW/cm² at 40°C. The stability test of the fuel cell showed that the materials used for the membrane-electrode assembly allowed more than 100 h of continuous operation with constant working characteristics.     

On the use of surface-confined molecular catalysts in fuel cell development

Fuel cells have the potential to provide sustainable clean energy but are hampered by the reliance on Pt as an electrocatalyst for half-cell reactions. Bio-inspired molecular catalysts, composed of Earth-abundant elements, have shown promise as alternative electrocatalysts for fuel oxidation and oxygen reduction reactions. This article provides a concise overview of recent progress in this area with particular focus on (i) electrodes modified with molecular catalysts for fuel oxidation and O₂ reduction and (ii) fuel cells incorporating surface-confined molecular catalysts for both anodic and cathodic reactions. Finally, the prospect and challenges of using molecular catalysts in fuel cell assemblies are discussed.     

Carbon-supported IrSn catalysts for a direct ethanol fuel cell

Carbon-supported Ir₃Sn/C and Ir/C catalysts were simply prepared with NaBH₄ as a reducing agent under the protection of ethylene glycol at room temperature. TEM and X-ray diffraction (XRD) data showed that the catalysts with small particle size exhibited the typical characteristic of a crystalline Ir fcc structure. Their electro-catalytic activities in comparison with Pt/C and Pt₃Sn/C catalysts also prepared by the NaBH₄ reduction process were characterized by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) techniques. The results indicated that Ir-based catalysts showed superior electro-catalytic activity towards ethanol oxidation to Pt/C and Pt₃Sn/C catalysts, mainly at low potential region. During single-cell tests at 90 °C, better performances of Ir-based catalysts as anodes were obtained compared to that of Pt/C catalyst. The comparable overall performance of Ir₃Sn/C to Pt₃Sn/C makes it a promising alternative choice of anode catalyst for direct ethanol fuel cells.     

Oxide supported platinum electrocatalysts for hydrogen and alcohol fuel cells

Efficient oxide supported electrocatalysts for hydrogen and alcohol fuel cells are developed. They are characterized by a low content of platinum, exhibit high activity in the oxidation of low-molecular alcohols and tolerance to the CO poisoning. It is shown that the application of catalysts developed (Pt/SnO₂-SbO _x ) enables one to raise the power of fuel cells operating on ethanol approximately by two times as compared with similar fuel cells with commercial PtRu/C catalysts.     

碳黑预处理对Pt/C催化剂对甲醇氧化电催化活性的影响

直接甲醇燃料电池(DMFC)由于具有较多的优点而受到广泛的关注. 但是碳载Pt (Pt/C)阳极催化剂电催化活性低是限制其应用的一个主要问题. 为了提高Pt/C催化剂对甲醇氧化的电催化性能, 分别用CO₂, 空气, H₂O₂或HNO₃对常用作为载体的Vulcan XC-72碳黑进行预处理. 结果表明, 在用CO₂, 空气, HNO₃, H₂O₂处理的及未处理的碳黑作载体制得的Pt/C催化剂电极上, 甲醇氧化峰的峰电流密度顺序为39, 33, 32, 20和18 mA•cm^－2, 表明用CO₂处理的碳载体制备的Pt/C催化剂对甲醇氧化有最好的电催化活性和稳定性. 其主要原因是用CO₂处理能减少碳黑表面的含氧基团和增加石墨化程度, 而使碳黑的电阻降低及Pt粒子在碳黑上的分散性变好.     

Anodic and Cathodic Platinum Dissolution Processes Involve Different Oxide Species

The degradation of Pt-containing oxygen reduction catalysts for fuel cell applications is strongly linked to the electrochemical surface oxidation and reduction of Pt. Here, we study the surface restructuring and Pt dissolution mechanisms during oxidation/reduction for the case of Pt(100) in 0.1 M HClO₄ by combining operando high-energy surface X-ray diffraction, online mass spectrometry, and density functional theory. Our atomic-scale structural studies reveal that anodic dissolution, detected during oxidation, and cathodic dissolution, observed during the subsequent reduction, are linked to two different oxide phases. Anodic dissolution occurs predominantly during nucleation and growth of the first, stripe-like oxide. Cathodic dissolution is linked to a second, amorphous Pt oxide phase that resembles bulk PtO₂ and starts to grow when the coverage of the stripe-like oxide saturates. In addition, we find the amount of surface restructuring after an oxidation/reduction cycle to be potential-independent after the stripe-like oxide has reached its saturation coverage.     

Anodic Electrocatalysts for Fuel Cells Based on Pt/Ti<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ru<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript>

The electrocatalytic activity of materials in the 10% Pt/Ti_1–xRu _x O_2–δ system, where x = 0–0.3 (0 ≤ Ru ≤ 30 mol %), in the reactions of hydrogen electrooxidation in the presence of CO is studied in the liquid three-electrode cell and a model of fuel cell. It is shown that the tolerance of the electrocatalysts towards CO is determined by the crystal structure of the support: the support with the rutile structure provides a higher rate of CO desorption than the support with the anatase structure. The potential of the onset of CO oxidation decreases with increasing concentration of dopant in the support from 650 mV for 10% Pt/TiO₂ to 480 mV (NHE) for 10% Pt/Ti_0.91Ru_0.09O_2–δ (rutile). The use of these materials as the anodic catalysts of fuel cell operating with hydrogen containing 30 ppm CO enabled us to obtain a current density by 7 times higher as compared with the 20% PtRu/C E-Tec catalysts.     

Ethanol electro-oxidation on catalysts with TiO2 coated carbon nanotubes as support

Pt–TiO₂/CNTs electrocatalysts for direct ethanol fuel cells (DEFCs) were prepared by sol–gel and ethylene glycol reduction method. XRD and TEM showed that the size of the Pt particles on TiO₂/CNTs is 3.5–4 nm and with narrow particle size distribution. HRTEM revealed that a thin layer of uniform amorphous TiO₂ on CNTs was formed and the faces of the Pt crystal on Pt–TiO₂/CNTs catalysts were quite “rough” and “rounded” and some grain bounders and/or twins also appeared. The electrochemical studies using cyclic voltammetry (CV), chronoamperometry and CO stripping voltammetry indicate that Pt–TiO₂/CNTs catalysts have higher electro-catalytic activity and CO-tolerance for ethanol oxidation than Pt/C (20 wt% Pt, E-TEK) and Pt/CNTs catalyst in acid. The Pt/TiO₂ molar ratio was also optimized and proved that 1:1 was the best Pt/TiO₂ molar ratio.     

Electrochemical processes on multi-component cathodic catalysts PtM and PtM<Subscript>1</Subscript>M<Subscript>2</Subscript> (M = Co,Ni, Cr): the effect of surface composition on the catalyst stability and its activity in O<Subscript>2</Subscript> reduction

The multi-component nanocatalysts based on platinum-transient metals alloys applied onto dispersed carbon material are considered as the most promising catalysts, which can be substituted for platinum in the fuel cell cathodes. The electrocatalytic activity of platinum in the PtM₁/C and PtM₁M₂/C alloys increases by several times with simultaneous increase in the stability. From the results obtained by structural and electrochemical methods, it is found that the synthesized binary and ternary catalysts are the metal alloys, whose surface is enriched in platinum as a result of surface segregation and subsequent chemical or electrochemical treatment. Under the corrosive attack, the less-noble metal, which has not entered into the alloy, dissolves, and the core-shell structures form. The properties of platinum in the shell differ from its properties in Pt/C due to the ligand effect of the core (metal alloy). As a result, the surface coverage with oxygen chemisorbed from water decreases in the binary and ternary systems. This causes an increase of the catalytic activity in the O₂ reduction reaction due to a decline in the effect of surface blocking against molecular oxygen adsorption and a decrease in the platinum dissolution rate, because the oxidation of platinum by water is the onset of corrosion process. For the catalytic systems studied, the mass activity decreases in the following order: 20% Pt in PtCoCr/C > 7.3% Pt in PtCo/C ≥ 7.3% Pt in PtCr/C and PtNi/C ≥ 40% Pt/C. The application of PtCoCr/C catalyst as the cathode in a low-temperature hydrogen-air fuel cell enabled one to reduce the platinum consumption by one half on retention of its performance.     

Porous carbon as electrode material in direct ethanol fuel cells (DEFCs) synthesized by the direct carbonization of MOF-5

Porous carbon (PC-900) was prepared by direct carbonization of porous metal-organic framework (MOF)-5 (Zn₄O(bdc)₃, bdc?=?1,4-benzenedicarboxylate) at 900 °C. The carbon material was deposited with PtM (M?=?Fe, Ni, Co, and Cu (20 %) metal loading) nanoparticles using the polyol reduction method, and catalysts PtM/PC-900 were designed for direct ethanol fuel cells (DEFCs). However, herein, we are reporting PtFe/PC-900 catalyst combination which has exhibited superior performance among other options. This catalyst was characterized by powder XRD, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and selected area electron diffraction (SAED) technique. The electrocatalytic capability of the catalyst for ethanol electrooxidation was investigated using cyclic voltammetry and direct ethanol single cell testing. The results were compared with those of PtFe and Pt supported on Vulcan XC72 carbon catalysts (PFe/CX-72 and Pt/XC-72) prepared via the same method. It has been observed that the catalyst PtFe/PC-900 developed in this work showed an outstanding normalized activity per gram of Pt (6.8 mA/g Pt) and superior power density (121 mW/cm² at 90 °C) compared to commercially available carbon-supported catalysts.     

Kinetics of mixed-controlled oxygen reduction at nafion-impregnated Pt-alloy-dispersed carbon electrode by analysis of cathodic current transients

The effects of Co alloying to Pt catalyst and Nafion pretreatment by NaClO₄ solution on the rate-determining step (RDS) of oxygen reduction at Nafion-impregnated Pt-dispersed carbon (Pt/C) electrode were investigated as a function of the potential step ΔE employing potentiostatic current transient (PCT) technique. For this purpose, the cathodic PCTs were measured on the pure Nafion-impregnated and partially Na⁺-doped Nafion-impregnated Pt/C and PtCo/C electrodes in an oxygen-saturated 1 M H₂SO₄ solution and analyzed. From the shape of the cathodic PCTs and the dependence of the instantaneous current on the value of ΔE, it was confirmed that oxygen reduction at the pure Nafion-impregnated electrodes is controlled by charge transfer at the electrode surface mixed with oxygen diffusion in the solution below the transition potential step |ΔE _tr| in absolute value, whereas oxygen reduction is purely governed by oxygen diffusion above |ΔE _tr|. On the other hand, the RDS of oxygen reduction at the partially Na⁺-doped Nafion-impregnated electrodes below |ΔE _tr| is charge transfer coupled with proton migration, whereas above |ΔE _tr|, it becomes proton migration in the Nafion electrolyte instead of oxygen diffusion. Consequently, it is expected in real fuel cell system that the cell performance is improved by Co alloying since the electrode reaches the maximum diffusion (migration) current even at small value of |ΔE|, whereas the cell performance is aggravated by Nafion pretreatment due to the decrease in the maximum diffusion (migration) current.     

Carbon nanotubes as efficient catalyst supports for fuel cells with direct ethanol oxidation

Several carbon materials, namely, single-walled nanotubes (CNT1), two-walled nanotubes (CNT2), multiwalled nanotubes (CNT3), and nanofibers (CNF) are synthesized by methane pyrolysis. The resulting nanomaterials are characterized by physical (BET) and electrochemical (charging curves) methods. A catalyst of ethanol electrooxidation PtSn (3: 1, 40 wt % Pt) that involves the mentioned nanomaterials as the supports is synthesized. The catalyst formed on two-walled nanotubes demonstrates the highest activity in ethanol oxidation under model conditions. X-ray diffraction analysis is used in studying the PtSn (3: 1, 40 wt % Pt)/CNT2 catalyst structure. The attained depth of ethanol oxidation is determined by the gas-liquid chromatography. Tests of an ethanol-oxygen fuel cell (FC) with the anodic active layer (AL) based on this catalyst are carried out.     

Au Nanoparticles Modified with Pt,Ru and SnO2 as Electrocatalysts for Ethanol Oxidation Reaction in Acids

The anodic reaction in direct ethanol fuel cells (DEFCs), ethanol oxidation reaction (EOR) faces challenges, such as incomplete electrooxidation of ethanol and high cost of the most efficient electrocatalyst, Pt in acidic media at low temperature. In this study, core‐shell electrocatalysts with an Au core and Pt‐based shell (Au@Pt) are developed. The Au core size and Pt shell thickness play an important role in the EOR activity. The Au size of 2.8 nm and one layer of Pt provide the most optimized performance, having 6 times higher peak current density in contrast to commercial Pt/C. SnO₂ as a support also enhances the EOR activity of Au@Pt by 1.73 times. Further modifying the Pt shell with Ru atoms achieve the highest EOR current density that is 15 and 2.5 times of Pt/C and Au@Pt. Our results suggest the importance of surface modification in rational design of advanced electrocatalysts.     

Pt4ZrO2/C cathode catalyst for improved durability in high temperature PEMFC based on H3PO4 doped PBI

In this paper, Pt₄ZrO₂/C was prepared and compared with commercial Pt/C (46.6 wt.% TKK) in terms of the durability as cathode catalyst in a high temperature proton exchange membrane fuel cell (PEMFC) based on H₃PO₄ doped polybenzimidazole (PBI) by a potential sweep test. The catalysts before and after the potential sweep test were characterized by rotating disk electrode (RDE), X-ray diffraction (XRD), transmission electron microscopy (TEM) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). After 3000 cycles potential sweep test, the overall performance loss of the Pt₄ZrO₂/C membrane electrode assembly (MEA) was less than that of the Pt/C MEA. The RDE results demonstrated that the oxygen reduction reaction (ORR) activity of the as-prepared Pt₄ZrO₂/C is nearly the same as TKK-Pt/C. The XRD and TEM results showed that Pt₄ZrO₂/C catalyst presented higher sintering resistance than commercial Pt/C catalyst during the potential sweep test. This may be attributed to the addition of ZrO₂, which acts an anchor to inhibit the adjacent platinum particles to agglomerate. The ICP-AES results of Pt₄ZrO₂/C cathode catalyst before and after the potential sweep test showed that the composition of Pt and Zr were very near the nominal atomic ratio of Pt:Zr, which reflected that Pt₄ZrO₂/C catalyst had a good stability during the potential sweep test. In brief, the preliminary results indicate that Pt₄ZrO₂/C catalyst is a good candidate of Pt/C catalyst in high temperature PEMFC based on H₃PO₄ doped PBI for achieving longer cell life-time and higher cell performance.     

Catalysts of ethanol anodic oxidation for ethanol-air fuel cell with a proton-conducting polymer electrolyte

Synthesis techniques for binary PtSn, PdM (M = Sn, V, Mo) and ternary PtSnNi, PtRuSn catalysts of ethanol electrooxidation on highly dispersed carbon materials are suggested. The highest activity in the 0.5 M H₂SO₄ solution containing 1 M C₂H₅OH corresponds to the system of PtSn (3: 1, 40 wt % Pt) with the particle size of 2–4 nm and tin content in the alloy with platinum of about 6%. It was shown that the catalyst efficiency as regards ethanol oxidation depth decreases in the series of Pt > PtRu ≈ PtSn, and the catalyst activity by current forms the series of PtSn > PtRu > Pt. The membrane-electrode assembly (MEA) with the anodes on the basis of the PtSn (3: 1, 40 wt % Pt) catalyst had stable characteristics for 220 h at the current density of ∼50 mA/cm².