Highly stable N-containing polymer-based Fe/Nx/C electrocatalyst for alkaline anion exchange membrane fuel cell applications

A cost-effective electrocatalyst with high activity and stability was developed. The Fe-Nx and pyridinic-N active sites were embedded in nitrogen-doped mesoporous carbon nanomaterial by carbonization at high temperature. The electrocatalyst exhibited excellent electrochemical performance for the oxygen reduction reaction, with high onset potential and half-wave potential values (E_onset = 1.10 ?V and E_1/2 ?= ?0.944 ?V) than 20 ?wt % Pt/C catalyst (1.04 and 0.910 ?V). The mass activity of the Schiff base network (SNW) based SNW-Fe/N/C@800° electrocatalyst (0.64 ?mA ?mg^?1 @ 1 ?V) reached about half of the commercial Pt/C electrocatalyst (1.35 ?mA ?mg^?1 @ 1 ?V). The electrocatalyst followed the 4-electron transfer mechanism due to very low hydrogen peroxide yield (H₂O₂ ?< ?1.5%) was obtained. In addition, this electrocatalyst with dual active sites showed high stability during cyclic voltammetry and chronoamperometry measurements. More importantly, the electrocatalyst also demonstrated the power density of 266 ?mW ?cm^?2 in the alkaline anions exchange membrane fuel cell (AEMFC) test, indicating its prospective application for fuel cells.     

Nickel-introduced structurally ordered PtCuNi/C as high performance electrocatalyst for oxygen reduction reaction

Designing highly active and durable oxygen reduction reaction (ORR) electrocatalysts is essential for developing efficient proton-exchange membrane fuel cells (PEMFCs). In this work, ordered PtCuNi/C nanoparticles (NPs) were synthesized using an impregnation reduction method. This study shows that the incorporation of Ni in ordered PtCu/C can effectively adjust the electronic structure of Pt, thereby optimizing oxygen binding energy for the ORR. The obtained intermetallic ordered PtCuNi/C NPs significantly improved ORR activity and durability compared to ordered PtCu/C. Specifically, PtCu_0·5Ni_0·5/C-700 shows a mass activity of 1.29 ​A ​mg _Pt⁻¹ ​at 0.9 ​V vs. reversible hydrogen electrode (RHE), which is about 9.2 times higher than that of commercial Pt/C. PtCu_0.5Ni_0.5/C-700 is also shown to be competent cathode catalyst for a single-cell system exhibiting high power density (461 ​mW ​cm⁻²). This work demonstrates that ordered PtCu_0·5Ni_0·5/C-700 can be used as a highly active and durable ORR catalyst in PEMFCs.     

ZIF-derived Co–N–C ORR catalyst with high performance in proton exchange membrane fuel cells

Metal and nitrogen-doped carbon (M-N-C) materials have been considered as the most promising non-precious metal oxygen reduction (ORR) catalysts to replace expensive Pt catalysts. Due to high Fenton catalytic activity of Fe element and the resulting instability, Co-based N–C (Co–N–C) catalysts without Fenton catalytic activity should be a worthier ORR catalyst being explored. Although the high ORR activity of Co–N–C catalyst has been demonstrated in aqueous half-cell tests, their performance under PEMFC working condition is still far away from that of state-of-the-art Fe–N–C catalysts. In this study, a high-performance Co–N–C catalyst was synthesized by one-step pyrolyzing Co-doped ZIF-8 (zeolitic imidazolate framework-8) particles in-situ grown on the high-surface-area KJ600 carbon black with high electronic conductivity. The resulting Co–N–C catalyst exhibited high intrinsic ORR activity, fast mass transfer rate and high electronic conductivity, and thus yielded a remarkable peak power density of 0.92 W cm^-2 in H₂–O₂ PEMFC, which is comparable to state-of-the-art Fe–N–C catalyst. This strategy is helpful to synthesize highly active M-N-C ORR catalysts with improved mass transfer and electric conductivity.     

FeCo-based mesoporous carbon shells modified N-doped porous carbon spheres for oxygen reduction reaction

FeCo-based non-noble metal electrocatalysts (NNMEs) of FeCo/MCS-NPCS was fabricated by immobilization of hemin on mesoporous carbon shells modified N-doped porous carbon spheres (MCS-NPCS). The obtained FeCo/MCS-NPCS exhibits a half-wave potential (E_1/2) of 0.851 ​V versus the reversible hydrogen electrode (vs. RHE) and a limited-diffusion current density (J_L) of 5.45 ​mA ​cm⁻². In addition, FeCo/MCS-NPCS shows comparable oxygen reduction reaction (ORR) performances to 20 ​wt% Pt/C in terms of E_1/2 and J_L and better electrochemical properties, including the methanol tolerance and durability in alkaline solution. Such outstanding electrochemical activities of FeCo/MCS-NPCS can be ascribed to Fe and/or Co-based nitrides and carbides as well as N-doped carbon matrixes modified with mesoporous carbon shells. This research introduces a promising path to design and synthesize highly efficient FeCo–N–C electrocatalysts towards ORR.     

Pyrolysis of Iron(III) porphyrin coated Pt/C toward oxygen reduction reaction in acidic medium

Design and synthesis of highly active and durable electrocatalysts toward oxygen reduction reaction (ORR) is of particular importance for proton exchange membrane fuel cells (PEMFCs), yet remains a grand challenge. Herein, we report the deposition of iron (III) porphyrin (FeP) on house-made Pt/C by rotary evaporation of the mixture of FeP and house-made Pt/C dispersed in chloroform, followed by pyrolysis at 650 °C in argon atmosphere. This approach led to the synthesis of new non-precious metal electrocatalyst (NPME)-Pt/C composites (Pt/C–FeP) with an average nanoparticle diameter of 3.1 ± 1.5 nm without aggregation. According to X-ray photoelectron spectroscopy (XPS), the binding energy of Pt 4f_7/2 became larger due to the presence of pyrolyzed FeP. In addition, the electrochemically active surface area (ECSA) of Pt/C–FeP-650 is 65 m²/g less than that of house-made Pt/C (80.2 m²/g). This implies that the pyrolyzed FeP may have partially covered the surface of Pt nanoparticles and thus lowering the ECSA. Interestingly, the mass activity (MA) of Pt/C–FeP turns out to be 349.0 mA/mg_Pt @0.9 V vs. RHE, which is 2.6 times and 1.5 times of house-made Pt/C and commercial Pt/C, respectively. It is speculated that the electronic interaction and possible synergy between Pt and pyrolyzed FeP as NPME might have contributed to the ORR activity improvement despite of partial loss of ECSA. During accelerated durability tests (ADTs), the MA of Pt/C–FeP-650 degrades 64.3% inferior to commercial Pt/C (52.2%). The main reason likely arises from the degradation of pyrolyzed FeP, which is a bottleneck problem confronting NPMEs.     

Large specific surface area S-doped Fe–N–C electrocatalysts derived from Metal–Organic frameworks for oxygen reduction reaction

It is highly desired but challenging to develop platinum group metal-free electrocatalysts for oxygen reduction reaction (ORR), which can promote the commercialization of fuel cell technology. To achieve this target, we report a one-step doping method to prepare S-doped Fe–N–C catalysts using zeolite imidazole framework (ZIF-8) and iron (III) thiocyanate (Fe(SCN)₃) as precursor. Different from conventional doping approach, i.e. physical mixing, Fe(SCN)₃ is in-situ added during ZIF-8 formation which would encapsulate Fe(SCN)₃ molecules inside ZIF-8 to avoid structure destruction and create potential replacement of Zn ions by Fe ions to form uniform Fe–N₄ complexes. As a result, the prepared S-doped Fe–N–C catalysts own large specific surface areas with a maximum value of 1326 ​m² ​g⁻¹ and a dual-scale porous structure that benefits mass transport. Significantly, the composition-optimized catalyst exhibits superior ORR activity in both 0.1 ​M HClO₄ electrolyte and 0.1 ​M KOH electrolyte, in which the half-wave potential reaches 0.81 ​V and 0.92 ​V (vs. RHE), respectively. Remarkable stability is also attained, which loses 2 ​mV only after 10000 potential cycles in O₂-saturated 0.1 ​M HClO₄ and remains almost constant in O₂-saturated 0.1 ​M KOH, surpassing commercial Pt/C catalyst in both acidic and alkaline medium.     

Cu2O-templated fabrication of Ni(OH)2·0.75H2O hollow tubes for electrocatalytic oxygen evolution reaction

Cu₂O is an ideal template material for the preparation of transition metal hydroxide/oxyhydroxides with oxygen evolution reaction (OER) enhanced catalytic performance. Here, inspired by Pearson's principle, Cu₂O wires were prepared and used as a sacrificial template to prepare Ni(OH)₂·0.75H₂O hollow tubes (Ni(OH)₂ HTs) with highly improved surface roughness. Benefiting from unique structural advantages, the Ni(OH)₂ HTs showed excellent catalytic activity, rapid kinetics and a long-term stability as the OER catalyst, where an overpotential of only 207 ?mV was required to drive a current density of 10 ?mA ?cm^?2, an ideal kinetics with a Tafel slope as 79.8 ?mV dec^?1 was calculated, and no obvious attenuation in chronoamperometry was discovered after operation for 24 ?h. This paper provides a novel template-assisted strategy to prepare high-performance transition metal-based OER catalysts possessing hollow and tubular structures.     

高温水热法合成系列介孔氧化铝负载铂催化

采用高温水热法制备稳定、 高度晶化的介孔氧化铝材料(M-Al₂O₃-n), 通过异丙醇铝前驱体与聚四乙烯基吡啶(P4VP)模板间的酸碱自组装实现材料介孔结构的构筑, 再经高温水热处理（180 ℃）实现孔壁的晶化, 并通过担载少量的铂活性组分研究其在催化完全燃烧苯中的性能. 结果表明: M-Al₂O₃-n具有高度晶化的孔壁结构和典型的γ-Al₂O₃晶型; M-Al₂O₃-n具有较大的比表面积（335 m²/g）、 孔容(1.36 cm³/g)和均一的孔径分布（16.1 nm）; M-Al₂O₃-n具有粗糙的表面结构及丰富的纳米多孔结构; 该材料负载少量的铂（质量分数为03%）活性组分得到的新型催化材料在较温和的条件下即可将苯类VOCs完全催化燃烧.     

Nitrogen-doped graphene nanosheets as high efficient catalysts for oxygen reduction reaction

It is of great significance in exploring alternative catalysts to platinum (Pt)-based materials for oxygen reduction reaction (ORR),because this reaction is invariably involved in various fuel cells and metal-air batteries.We herein reported the nitrogen doped graphene nanosheets (NGNSs) with pore volume of as high as 3.42 m 3 /g and investigated their potential application as ORR catalysts,it was demonstrated the NGNSs featured high activity,improved kinetics and excellent long-term stability for ORR.The NGNSs were successfully used as cathode catalysts of microbial fuel cells (MFCs) and performed even better than the commercial Pt/C (Pt 10%) catalysts at the maximum power output.     

Enhanced low-humidity performance of proton-exchange membrane fuel cell by introducing hydrophilic CNTs in membrane electrode assembly

Hydrophilic carbon nanotubes (HCNTs) were introduced into the membrane electrode assembly (MEA) to improve its low-humidity performance. The effects of types, placement, loading, and relative humidity on the MEA performance were investigated. It has been found that the MEA with 20 ?wt% HCNTs loading both in anode and cathode achieved the best self-humidifying performance. Its current density reached 1550 ?mA ?cm^?2 at 0.6 ?V, with a maximum power density of 953 ?mW/cm² at 70 ?°C, 30 psi and 30% relative humidity conditions. Besides, the stability test shows that its current density at 0.6 ?V only decreased by 6.4% after 44 ?h performance test, while the performance of blank MEA without HCNTs decreased by 45% within 6 ?h testing period. This extraordinary performance under low humidity condition is ascribed to that the HCNTs contained in the MEA improve the water management and mass transportation by functioning as a dispersant and hydrophilic agent.     

Effect of Ce addition on hot corrosion behaviours of a cast γ′-strengthened Co–Al–W–Mo–Ta–B alloy at 800 ​°C

Hot corrosion behaviours of a novel Co–9Al-4.5W-4.5Mo–2Ta-0.02B alloy doped with 0.01, 0.05, 0.1 and 0.2 ?at% Ce exposed at 800 ?°C in a solution of 75%Na₂SO₄/25%NaCl were investigated. The alloys comprised a coherent γ-Co_SS/γ′-Co₃(Al, W) microstructure (0.01Ce and 0.05Ce alloys) and κ-Co₃(W, Mo) precipitates (0.1Ce and 0.2Ce alloys) at grain boundaries. Hot corrosion kinetics curves demonstrated the parabolic time dependency profile with two stages: the first parabolic stage is within the beginning ～50 ?h corrosion and follows by the second parabolic stage. With an increasing nominal Ce content the weight gain of the alloy significantly decreased from approximately 70.1 ?mg ?cm^?2 (0.01Ce) to 40.8 ?mg ?cm^?2 (0.2Ce) when exposed for 100 ?h. A two-layer corrosion scale formed, and the scale was composed of an outer layer of Co₃O₄ oxide with spinel compounds of CoAl₂O₄, CoWO₄and CoSO₄, and an inner γ/needle-like Co₃W/sulphide layer adhered to the substrate. Heavy spallation of the corrosion scale occurred in the 0.01Ce～0.1Ce alloys, however, spallation was slight in the 0.2Ce alloy. The excellent corrosion resistance of the 0.2Ce alloy could be attributed mainly to the formation of continuous Al₂O₃ lines in the corrosion scale, as well as the prolongation of the incubation period of the corrosion product spallation.     

Hydrothermal synthesis of hydroxyapatite coating on the surface of medical magnesium alloy and its corrosion resistance

The early corrosion control of biomedical magnesium alloy is an important measure to determine its good performance during implantation into human body. The deposition of calcium phosphate biological coating is the most effective solution at present. In this paper, hydroxyapatite (HAP) coating was hydrothermal synthesized on the surface of AZ31B magnesium alloy, and the influence mechanism of hydrothermal synthesis temperature, time and solution concentration was investigated. The synthesis conditions and deposition mechanism of hydroxyapatite coating without DCPA (CaHPO₄) were proposed. The surface morphology of the coating was observed by field emission electron scanning microscope (FESEM). The types and contents of microelements in the material were analyzed by energy disperse spectroscopy (EDS). Fourier transform infrared spectroscopy (FTIR) was used to analyze the functional group information of the coating surface. The corrosion resistance of different experimental groups was studied by electrochemical test. The results showed that when the calcium phosphate solution concentration was 0.1 ?mol/L and the calcium/phosphorus ratio was 1.67, the coating had better morphology structure and corrosion resistance, and the calcium/phosphorus ratio of HAP crystals reached 1.58, the epit of the prepared AZ31B-HAP coating by bare metal increased from ?1.51 ?V to ?1.18 ?V, the impedance value reached 1.0 ?× ?10⁵ ?Ω?cm², and the early corrosion of magnesium alloy substrate was effectively delayed.     

Magnetic field induced synthesis of (Ni,Zn)Fe2O4 spinel nanorod for enhanced alkaline hydrogen evolution reaction

Recently, the introduction of external fields(light, thermal, magnetism, etc.) during electrocatalysis reactions gradually becomes a new strategy to modulate the catalytic activities. In this work, an external magnetic field was innovatively employed for the synthesis progress of(Ni, Zn)Fe₂O₄spinel oxide(M-(Ni, Zn)Fe₂O₄). Results indicated the magnetic field(≤250 m T) would affect the morphology of catalyst due to the existing Fe ions, inducing the M-(...     

Bimetal nickel–cobalt phosphide directly grown on commercial graphite substrate by the one-step electrodeposition as efficient electrocatalytic electrode

It is challenging to find a method to obtain a catalyst with low cost and efficient multifunctional performances. Herein, in order to obtain the electrode with high-performance water splitting and non-enzymatic glucose detection, the commercial graphite sheet (GS) with excellent durability and electroconductivity was used as substrate material, and the non-noble ternary component Ni–Co–P catalyst with hierarchical architecture was fabricated on GS via a co-electrodeposition. The catalyst only required low overpotentials of 44.6, 76.5 and 49 mV to drive the current density of 10 mA cm⁻² alongside with the smaller Tafel slopes of 39.2, 44.8 and 112 mV dec⁻¹ for hydrogen evolution reaction (HER) in 1.0 M KOH, 0.5 M H₂SO₄ and 1.0 M PBS solution, respectively. For oxygen evolution reaction (OER), the catalyst demonstrated a low overpotential of 304 mV to achieve the current density of 20 mA cm⁻² with excellent Tafel slope of 89.8 mV dec⁻¹ in alkaline solution. Furthermore, the Ni–Co–P/GS electrode serving as non-enzymatic glucose sensor exhibited the superior electrocatalytic activity with an ultrahigh sensitivity of 7400 μA mM⁻¹ cm⁻², low detection limit of 0.425 μM (S/N = 3), and wide linear range (1–1200 μM).     

Corrosion resistance and thermal stability of sputtered Fe44Al34Ti7N15 and Al61Ti11N28 thin films for prospective application in oil and gas industry

Fe-and Al-based thin-film metallic glass coatings (Fe₄₄Al₃₄Ti₇N₁₅ and Al₆₁Ti₁₁N₂₈) were fabricated using magnetron co-sputtering technique, and their corrosion performances compared against wrought 316L stainless steel. The results of GI-XRD and XPS analyses demonstrated amorphous structure and oxide layer formation on the surface of the fabricated thin films, respectively. The potentiodynamic (PD) polarization test in chloride-thiosulfate (NH₄Cl ​+ ​Na₂S₂O₃) solution revealed lower corrosion current (I_corr) (0.42 ​± ​0.02 ​μA/cm² and 0.086 ​± ​0.001 ​μA/cm² Vs. 0.76 ​± ​0.05 ​μA/cm²), lower passivation current (I_pass) (1.45 ​± ​0.03 ​μA/cm² and 1.83 ​± ​0.07 ​μA/cm² Vs. 1.98 ​± ​0.04 ​μA/cm²), and approximately six-fold higher breakdown potential (E_bd) for Fe- and Al-based coatings than those of wrought 316L stainless steel. Electrochemical Impedance Spectroscopy (EIS) of both films showed 4- and 2-fold higher charge transfer resistance (R_ct), 7- and 2.5-times higher film resistance (R_f), lower film capacitance values (Q_f) (10 ​± ​2.4 ​μS-s^acm^-2, and 5.41 ​± ​0.8 ​μS-s^acm^-2 Vs. 18 ​± ​2.21 ​μS-s^acm^-2), and lower double-layer capacitance values (Q_dl) (31.33 ​± ​4.74 ​μS-s^acm^-2, and 15.3 ​± ​0.48 ​μS-s^acm^-2 Vs. 43 ​± ​4.23 ​μS-s^acm^-2), indicating higher corrosion resistance of the thin films. Cyclic Voltammetry (CV) scan exhibited that the passive films formed on the Fe- and Al-based coatings were more stable and less prone to pitting corrosion than the wrought 316L stainless steel. The surface morphology of both films via SEM endorsed the CV scan results, showing better resistance to pitting corrosion. Furthermore, the thermal analysis via TGA and DSC revealed the excellent thermal stability of the thin films over a wide temperature range typically observed in oil-gas industries.     

纳米Pt/Graphene复合电极的制备及对甲醇电催化性能的影响

采用一步还原法制备直接甲醇燃料电池纳米Pt/graphene (Pt/G)阳极. XRD和SEM表征表明Pt纳米均匀分散于石墨烯表面.循环伏安和计时电流的电化学测定结果表明:复合纳米Pt/G的催化活性和稳定性优于纯铂;采用计时电量法测定298 K时甲醇在硫酸溶液中扩散系数为1.37×10-9 cm2·s-1,以及在不同阶跃电位下甲醇催化氧化反应速率常数k_f.      

Flexible micro-supercapacitors fabricated from MnO2 nanosheet/graphene composites with black phosphorus additive

Supercapacitors are widely used for powering flexible/wearable electronics owing to their excellent charge storage capabilities. In this study, MnO₂ nanosheets were grown on the surface of graphene using a simple water bath method to prepare graphene/MnO₂ composites for fabricating supercapacitors. In addition, two-dimensional black phosphorus was introduced as an additive into the electronic ink based on the as-prepared graphene/MnO₂ composites. The characterization and electrochemical analyses results showed that adding black phosphorus considerably improved the capacitive performance of the material, yielding a high specific capacitance of 241.5 ?F ?g^-1 at 0.1 ?A ?g^-1 and an impressive rate capability improvement from 52.5% to 80.3%. Then the micro-supercapacitor having an area-specific capacitance of 20.15 ?mF ?cm^-2 at a scanning rate of 2 ?mV ?s^-1 was utilized to demonstrate the practical applicability of this material. To further evaluate the practical applicability of this micro-supercapacitor, the micro-supercapacitor was integrated with a flexible thin-film pressure sensor on paper and cloth through screen printing.     

ZrO_2-supported α-MnO_2:Improving low-temperature activity and stability for catalytic oxidation of methane

The single phaseα-Mn O_2and in-situ supportedα-Mn O_2/Zr O_2with different ratios of Mn/Zr were synthesized by one-pot hydrothermal method.They showed superior activity for catalytic oxidation of methane and even better than that of 1%Pt/Al_2O_3.The T_(50)of Mn O_2/Zr O_2catalysts with different ratios of Mn/Zr were located in the range of 315–335°C at a WHSV of 90 L g~(-1)h~(-1),whereas that of Pt/Al_2O_3was 380°C.After sulfur ageing,the Mn O_2/Zr O_2catalysts with Mn/Zr ratio of 2:1(2Mn O_2/1Zr O_2)and 1:1(1Mn O_2/1Zr O_2)exhibited satisfying sulfur resistance in comparison to the pure Mn O_2.The 2Mn O_2/1Zr O_2catalyst also showed acceptable catalytic stability,and the addition of 10 vol%CO_2had no obvious negative effect on its stability,whereas the addition of2.6 vol%H_2O caused slight but reversible decreasing methane oxidative activity.     

Gas-Liquid Interfacial Plasma engineering under dilute nitric acid to improve hydrophilicity and OER performance of nickel foam

The world has been moving rapidly to find new eco-friendly energy sources. Water electrolysis consists of two reactions of Oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER), whereas the OER is considered the rate-limiting step. The most commercialized electrode for OER in the alkaline electrolyte is Ni foam, but its original surface is hydrophobic. It is possible to accelerate the adsorption and desorption process of reactants and products during OER by adding hydrophilic functional groups such as –OH on the surface of Ni foam. In this study, a novel Gas-Liquid Interfacial Plasma (GLIP) engineering at room temperature was successfully applied to modify the Ni foam surface dilute (1 ?M) HNO₃ solution. At a current density of 400 ?mA ?cm^?2, GLIP-treated Ni foam electrodes at 1 ?M HNO₃ concentrations showed OER overpotentials of 458 ?mV. Among all, GLIP with 1 ?M HNO₃ treatment of 30 ?min showed 129 ?mV less overpotential than the nickel foam before treatment. In summary, GLIP can be justified as an environmentally friendly and efficient surface treatment to improve the wettability and OER performance of Ni-based electrodes in water electrolysis.     

The synthesis and characterization of a Co-N/C composite catalyst for the oxygen reduction reaction in acidic solution

A non-precious metal Co-N/C catalyst for the oxygen reduction reaction (ORR) was synthesized by heating a mechanical mixture of cobalt chloride, urea and acetylene black under a nitrogen atmosphere. The catalyst was characterized by XRD and XPS. The electrocatalytic activity in the ORR was evaluated by linear sweep voltammetry in 0.5 mol L⁻¹ H₂SO₄ solution. The results show that the Co-N/C catalyst aids the reduction of oxygen. The presence of elemental cobalt in the precursor allows nitrogen atoms to embed themselves in the graphite matrix to form pyridinic and graphitic type C-N structures as the ORR active sites. The effect of heat-treating temperature on the catalytic activity was also investigated. The results also show that the Co-N/C catalyst is most active when pyrolyzed at 600°C. The obtained Co-N/C catalyst loses some activity after initial exposure to the H₂SO₄ solution because of leaching, but is then stable for up to 20 h immersion. The catalyst is also stable when charged, which is supported by the cyclic voltammetry results.