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Controllable development of cost-effective oxygen reduction reaction (ORR) catalysts with a bottom-up method is one of the primary remaining challenges in catalysis due to the complexity and random reaction among ingredient molecules. Herein, a B and N co-doped metal-free carbonaceous (BNC) catalyst with hierarchical porous structure and super high specific surface area was rationally constructed by a secondary pyrolysis method for the ORR. By comparatively analyzing the preparation parameter–structure relationship, the addition time of the B precursor was proved to have a key influence on the B doping content. Meanwhile, the secondary pyrolysis procedure endowed BNC with a large amount of homogeneous exposed N and B active species, abundant mass transfer nanopores, and high conductivity. Consequently, BNC provides an outstanding ORR activity with an onset potential of 0.94 V and a half-wave potential of 0.84 V, which are similar to those of Pt/C. More importantly, a BNC based Zn–air battery delivers high peak power density (115.5 mW cm−2) and good discharge stability (45 h).

Low‐volume power density remains a significant barrier to the portable application of direct methanol fuel cell (DMFC). Herein, a shared anode flow field (SAFF) structure is introduced in an active DMFC to reduce stack volume and improve discharge performance. The differences in discharge performance between the bi‐cell with SAFF and the bi‐cell with traditional anode flow field (TAFF), coupled with the effect of operating conditions on performance, are investigated by polarization curve, electrochemical impedance spectra, and voltage versus time curves. The results show that the SAFF structure enhances anode mass transfer, resulting in an improvement in peak power density and voltage stability of the bi‐cell compared to the TAFF structure. In addition, the bi‐cell with SAFF achieves its highest peak power density at a lower methanol concentration, alleviating the methanol crossover caused by high concentration. The SAFF structure is an attractive choice for DMFC portable applications. A bi‐cell with a shared anode flow field (SAFF) is designed and manufactured. The SAFF structure enhances the anode mass transfer process. Therefore, the volumetric power density of the bi‐cell with SAFF is increased due to its compact size and high peak power density. In addition, the bi‐cell with SAFF exhibits a more stable voltage.

Reversible oxygen catalysts with good catalytic performance and economic efficiency are urgently needed for the rapid development of metal–air batteries and reversible fuel cells. Herein, a metal-free N, S co-doped porous carbon thin film (NSCF) was coated in situon carboxylic carbon nanotubes (CNT@NSCF) viaa simple and scalable low temperature polymerization–high temperature pyrolysis strategy. By analyzing the surface structure of comparable carbon supports including ketjenblack, Vulcan XC-72 carbon, and activated carbon, it is found that the surface oxygen-containing functional groups of the support are the key factor to obtaining a uniform coating of NSCF with the formation of a large amount of efficient N, S active species. As a result, the optimal CNT@NSCF shows an excellent bifunctional oxygen catalytic activity with a narrow potential difference (ΔE= Ej= 10,OER− E1/2,ORR) value of 0.74 V, which is superior to that of Pt/C + RuO2(0.75 V) and most metal-free carbon-based oxygen catalysts. Notably, the CNT@NSCF-based rechargeable Zn–air battery delivers a remarkable performance with a high open-circuit voltage and outstanding charge–discharge stability after 213 h, which fully demonstrates the promising practical application potential of the CNT@NSCF catalyst.

The transient response of a high‐temperature proton exchange membrane fuel cell (HT‐PEMFC) is critical for control and optimization. The objective of this study is to investigate the effects of operating conditions and control parameters on the transient response of the HT‐PEMFC during load variations to optimize the operating conditions. The main causes of the voltage undershoot are investigated experimentally, and the effects of air stoichiometry, air humidity, operating temperature, and backpressure on the transient response of the HT‐PEMFC are evaluated in terms of internal resistance and voltage response. The results show that during load changes, the local gas starvation of the cell and the change in the hydration state of membrane‐electrode‐assembly may be the main cause of the voltage undershoot. The voltage drop is affected by the combination of ohmic resistance, charge transfer resistance, and mass transfer resistance. In addition, operating temperature and air stoichiometry can affect voltage drop and voltage undershoot during load changes. Proper humidification of the air can alleviate voltage undershoot problems. Increasing the backpressure can improve the transient performance of the cell, but does not alleviate the voltage undershoot problem. The study can provide guidelines for the design and control of HT‐PEMFC operating conditions. Herein, the voltage response of high‐temperature proton exchange membrane fuel cell (HT‐PEMFC) during load variation is investigated. The local gas starvation of cell and the change in the hydration state of membrane‐electrode‐assembly may be the main cause of the voltage undershoot. The influence of each operating condition on the dynamic response of a HT‐PEMFC is studied.

First-row transition metal compounds have been widely explored as oxygen evolution reaction (OER) electrocatalysts due to their impressive performance in this application. However, the activity trends of these electrocatalysts remain elusive due to the effect of inevitable iron impurities in alkaline electrolytes on the OER; the inhomogeneous structure of iron-based (oxy)hydroxides further complicates this situation. Bimetallic metal-organic frameworks (MOFs) have the advantages of well-defined and uniform atomic structures and the tunable coordination environments, allowing the structure-activity relationships of bimetallic sites to be precisely explored. Therefore, we prepared a series of iron-based bimetallic MOFs (denoted as Fe2M-MIL-88B, M = Mn, Co, or Ni) and systematically compared their electrocatalytic performance in the OER in this work. All the bimetallic MOFs exhibited higher OER activity than their monometallic iron-based counterpart, with their activity following the order FeNi > FeCo > FeMn. In an alkaline electrolyte, Fe2Ni-MIL-88B showed the lowest overpotential to achieve a current density of 10 mA cm−2(307 mV) and the smallest Tafel slope (38 mV dec−1). The experimental and calculated results demonstrated that iron and nickel exhibited the strongest coupling effect in the series, leading to modification of the electronic structure, which is crucial for tuning the electrocatalytic activity.

Fe-doped ZIF-8 is prepared by a microwave-assisted method, featured with fast, energy-saving and solvent-free. The derived Fe-N-C has abundant atomic FeN4sites dispersed on porous carbon, served as efficient ORR electrocatalysts for fuel cells.

Rational electrode design is crucial to promote the performance of the hydrogen evolution reaction (HER) via further enhancing the activity, stability, and utilization of platinum (Pt) in an alkaline electrolyte. Herein, a binder-free low-Pt-content HER electrode, Pt (∼20 μg cm–2) decorated on nickel hydroxide grown on nickel foam (Pt-Ni(OH)2-2h-NF20), is fabricated at near room temperature in a test tube. To lower the ohmic resistance, for the first time, the Pt nanoparticles were location-selectively anchored on the bottom of height-controlled vertical Ni(OH)2nanosheets via utilizing the mass transfer resistance of the dense Ni(OH)2film for chloroplatinate. Furthermore, the excellent mass transfer, high specific surface area of Pt, synergistic effect between Pt with Ni(OH)2, and stable structure together prompt the resulting electrode with a special structure to exhibit superior HER electrocatalytic activity and stability in 1 M KOH. Typically, this electrode reaches a current density of 35.9 mA cm–2at an overpotential of 100 mV, which is over 8 times higher than that of commercial Pt/C, and the overpotential only increases by 20 mV at 100 mA cm–2over 150,000 s of stability test. Benefiting from the simple fabrication process, the electrode with an area of 840 cm2was successfully prepared with a steady overpotential of 370 mV at 1000 mA cm–2and increased potential of 23 mV over 50 h of stability test.

Fabrication of novel electrode architectures with nanostructured ultrathin catalyst layers is an effective strategy to improve catalyst utilization and enhance mass transport for polymer electrolyte membrane fuel cells (PEMFCs). Herein, we report the design and construction of a nanostructured ultrathin catalyst layer with ordered Pt nanotube arrays, which were obtained by a hard-template strategy based on ZnO, via hydrothermal synthesis and magnetron sputtering for PEMFC application. Because of the crystallographically preferential growth of Pt (111) facets, which was attributed to the structural effects of ZnO nanoarrays on the Pt nanotubes, the catalyst layers exhibit obviously higher electrochemical activity with remarkable enhancement of specific activity and mass transport compared with the state-of-the-art randomly distributed Pt/C catalyst layer. The PEMFC fabricated with the as-prepared catalyst layer composed of optimized Pt nanotubes with an average diameter of 90(±10) nm shows excellent performance with a peak power density of 6.0 W/mgPtat 1 A/cm2, which is 11.6% greater than that of the conventional Pt/C electrode.

Hydrogen is a promising sustainable energy to replace fossil fuels owning to its high specific energy and environmental friendliness. Alkaline water electrolysis has been considered as one of the most prospective technologies for large scale hydrogen production. To boost the sluggish kinetics of hydrogen evolution reaction (HER) in alkaline media, abundant materials have been designed and fabricated. Herein, we summarize the key achievements in the development of layered transition-metal hydroxides [TM(OH)x] for efficient alkaline HER. Based on the structure of TM(OH)x, the mechanism of synergistic effect between TM(OH)xand HER active materials is illuminated firstly. Then, recent progress of TM(OH)x-based HER catalysts to optimize the synergistic effect are categorized as TM(OH)xand active materials, including species, structure, morphology and interaction relationship. Furthermore, TM(OH)x-based overall water splitting electrocatalysts and electrodes are summarized in the design principles for high activity and stability. Finally, some of key challenges for further developments and applications of hydrogen production are proposed.

The stability of a direct methanol fuel cell (DMFC) was investigated by two single DMFCs with different anode structure membrane electrode assembly (MEA) under discharging at the constant current model for more than 4000 h. One of the MEAs with a catalyst coating membrane (CCM) anode electrode loads 5.5 mg cm–2anode catalyst of Ru black loading, and the other with a gas diffusion layer coating (GDE) anode electrode loads 5.5 mg cm–2of 60% PtRu/C. During the stability testing, DMFC with a CCM anode structure with a noble metal loading (5.5 mg cm–2) showed a 22% performance loss and that of GDE anode structure with a lower noble metal loading (3.3 mg cm–2) was 17%. Polarization curves, electrochemical measurements, and EDX (energy dispersive X-ray spectroscopy) were performed to analyze the difference of catalyst activity, internal resistance, and Ru loss between two DMFCs.

•We propose a platinum in-situ catalytic oleylamine combustion removal strategy.•We offer thermogravimetric analysis as a sensitive technique to monitor the removal process.•The key parameters affecting the removal efficiency are isolated and systematically optimized.

Due to the unique structure, carbon aerogels have always shown great potential for multifunctional applications. At present, it is highly desirable but remains challenging to tailor the microstructures with respect to porosity and specific surface area to further expand its significance. A facile chemical foaming coupled self-etching strategy is developed for multiscale processing of carbon aerogels. The strategy is directly realized via the pyrolysis of a multifunctional precursor (pentaerythritol melamine phosphate) without any special drying process and multiple steps. In the micrometer scale, the macroporous scaffold structures with interconnected and strutted carbon nanosheets are built up by chemical foaming from decomposition of melamine, whereas the meso/microporous nanosheets are formed via self-etching by phosphorus-containing species. The delicately hierarchical structures and record-breaking specific surface area of 2668.4 m2g–1render the obtained carbon aerogels great potentials for absorption (324.1–593.6 g g–1of absorption capacities for varied organic solvents) and energy storage (338 F g–1of specific capacitance). The construction of such novel carbon nanoarchitecture will also shed light on the design and synthesis of multifunctional materials.

Highly rigid p-terphenyl units induce formation of moderate and tight PA aggregates reinforcing ion-pair interaction between piperidinium and biphosphate and alleviating the plasticization effect of PA.

Fabrication of novel electrode architectures with tailored electrochemical interfaces (EI) is an effective strategy for enhancing charge and mass transport processes within electrochemical devices. Here, we design and fabricate a well-hybrid electrode based on the coupling of polyaniline (PANI) nanowires and Pt-based electrocatalysts to manufacture a hybrid electric power device (HEPD) combining the advantages of supercapacitors and fuel cells. Because of the boosted charge transfer between PANI nanowires and Pt-based materials via enhanced EIs, the HEPD assembled with hybrid electrodes shows remarkable performance with a peak power density of 222 mW cm–2, a specific power of 3810 W kg–1, and a specific energy of 2100 Wh kg–1, normalized to the mass of membrane electrode assemblies. The in situ Raman spectra and extended electrochemical studies demonstrate the intrinsic mechanism of charge transfer processes within hybrid electrodes, shedding light on the alternative progress of electrochemical energy conversion systems and storage devices.

The chemical structure–effect relationship between imidazolium ion liquid and the properties of electrolyte or Al battery is first completely revealed. First, it is proved that there indeed exsits an interaction between imidazolium cation and chloroaluminate anions (active ions, Al2Cl7–and AlCl4–), blocking their reaction in the anode or positive electrode. Second, by introducing the substituent effect, which could enhance the steric hindrance and change the detailed electronic distribution of imidazolium cations, the intermolecular force between imidazolium cations and chloroaluminate anions is effectively weakened. As a result, the electrodeposition achievement, electrodeposition/electrostripping reversibility of aluminum, and intercalation/deintercalation capacity of AlCl4–in the positive electrode are significantly improved. Therefore, the as-assembled battery with AlCl3/[MPIM]Cl electrolyte shows an ∼100% CE. This work provides a potential approach on how to enhance the performance of Al battery by designing the ionic liquid structure.

Exploring advanced electrocatalysts to accelerate the sluggish oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs) is a promising route to alleviate the current challenges of fossil fuel exhaustion and environment pollution. Herein, a carbon-supported highly dispersed PtNi nanocatalyst (Pt0.61Ni/C) with low platinum content of 2.76 wt % was prepared simply based on galvanic replacement for a high-efficiency ORR process. It presents a mass activity of ∼5 times of the conventional Pt-based catalyst at 0.9 V (vs reversible hydrogen electrode (RHE)) and a remarkable durability and methanol tolerance. The acidic fuel cell with such cathode catalyst (Pt0.61Ni/C) presents a striking performance with maximum power density up to 1.1 W cm–2at 80 °C. Due to the extremely low platinum loading in the whole fuel cell, its Pt utilization (0.093 gPtkW–1) is the highest reported ever in H2/O2fuel cells. Such impressive performance of Pt0.61Ni/C makes the obtained Pt0.61Ni/C catalyst a very promising alternative to conventional Pt-based catalysts for their large-scale application in future.

With the increasing demand of energy storage towards increasing the use of renewable energy technologies, electrochemical systems with low cost, high safety levels, and low environmental impact are critically needed. Zinc–air/oxygen batteries, which were always considered to be cheap, are losing their competitive advantages due to poor cyclic performance and energy efficiency. Herein, an effective strategy for oxygen recycling, which reduces the cost of oxygen to as low as ¢ 0.2 kWh−1per cycle, is reported. With the use of oxygen, the performance of zinc–oxygen batteries is largely increased, with a maximum power density of 290 mW cm−2, stable cycling for more than 1500 cycles, an average energy density of 60 %, and elimination of carbonates. A 1 kW/1 kWh zinc–oxygen battery system is also integrated and exhibits a satisfactory energy efficiency of 58 % and a high working power density of 75 mW cm−2. Don't let the air out! An effective strategy of oxygen recycling is proposed to reduce the cost of oxygen per cycle. With the use of oxygen instead of air, the performance of zinc–oxygen batteries is increased with improved cycling stability. The integration of an oxygen recycling system and a zinc–oxygen battery system yields a satisfactory energy‐storage device.

The H3PO4poisoning problem severely limits the performance of high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs) using the H3PO4‐doped polybenzimidazole as electrolyte membrane. Herein, the micropore‐rich carbon shell‐confined Pt‐based nanoparticles (Pt@MPC) with a Pt loading of 44.9 wt% is developed as the H3PO4poisoning‐resistant electrocatalyst for oxygen reduction reaction (ORR), which possesses both high ORR activity and stability. The half‐wave potential (E1/2) of 0.898 V and electrochemical active surface area (ECSA) of 62.3 m2gPt−1are superior to commercial 40 wt% Pt/C (E1/2= 0.892 V; ECSA = 53.1 m2gPt−1). Pt@MPC remains almost unchanged after the accelerated durability test of 10 000 cycles. Moreover, Pt@MPC exhibits remarkable H3PO4tolerance as its negative shift of E1/2(82 mV) is less in H3PO4‐containing electrolyte compared with commercial Pt/C (114 mV). This can be attributed to the steric effect of the micropore‐rich carbon, which enables the selective transport of reactants while inhibiting H3PO4. The HT‐PEMFCs assembled with Pt@MPC (0.7 mgPtcm−2) exhibit a maximum power density of 674 mW cm−2under the H2‐O2condition and outperform the commercial Pt/C (616 mW cm−2). This strategy provides a new direction for the design of ORR catalysts toward HT‐PEMFCs with better phosphoric acid poisoning resistance. The phosphoric acid poisoning resistance in the oxygen reduction reaction catalyst is achieved through the confinement of Pt‐based nanoparticles in the micropore‐rich carbon (Pt@MPC). Due to the steric effect, the micropore‐rich carbon enables the selective transport of reactants while inhibiting the adsorption of phosphoric acid on the Pt surface and reduces the leaching and migration of Pt.

Ion migration and electron transfer are crucial phenomena in electrochemistry and interfacial sciences, which require effective coupling and integration of separated charge pathways within medium materials. Here, in this work, we fabricated an ordered nanowire material based on hybrid polymers of polypyrrole, with electronic conductance, and perfluorosulfonic acid ionomers, with ionic conductance, via a facile one-step electrochemical route. Because of the nanoconfined effects for the different charge-transfer channels within the nanowire polymer matrix, the electronic and ionic conductivities of the hybrid polymer are surprisingly enhanced, being 26.4 and 0.096 S cm–1, respectively. Such an improvement in the formation of charge pathways also leads to an increased electrochemical capacitance through enlargement of the area of ion/electron transport boundaries, which may show great potential in the applications of supercapacitors, fuel cells, rechargeable batteries, and other electrochemical devices.

Since distributions of water and phosphoric acid (PA) have significant influence on the performance of high temperature proton exchange membrane fuel cell (HT-PEMFC) and are difficult to be characterized by experiment, a nonisothermal multiphase model considering the effect of PA polycondensation on the proton conductivity is developed to investigate the influence of flow field structures and operating conditions on these distributions for a HT-PEMFC with area of 160 cm2. The results show that the flow field has little effect on discharge performance when pure hydrogen is feed. With the increase of anode stoichiometry, the PA concentration is elevated, which resulted in a lower proton conductivity. When current density increases from 200 to 600 mA cm–2, PA concentration (average value of MEA) decreases from 97.26 to 94.82 wt %. Although a higher temperature leads to aggravation of PA polycondensation, the proton conductivity is improved. With the increasing of water vapor composition of the anode feed, the PA is diluted and proton conductivity decreases.

Hydrogen starvation is one of the major challenges for practical application of fuel cells, which could seriously deteriorate the reliability and safety of the system with the occurrence of voltage reversal. High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) fed with reformate hydrogen are more liable to suffer from fuel starvation as a result of reduced hydrogen proportion and poisoning impurity of CO. To conquer this inconvenience, here, in this work, a non-uniform catalyst layer with a hydrogen storage function of palladium was developed according to the in-plane distribution characteristics of hydrogen. With the in situstorage and release of hydrogen within the lattice of palladium, fuel could be replenished at the site close to the outlet where fuel starvation could occur. As a result, the utilization of hydrogen is greatly promoted, and the voltage reversal caused by fuel starvation is also prohibited.

Carbon supported gold-iridium composite (AuIr/C) was synthesized by a facile one-step process and was investigated as the bifunctional catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The physical properties of the AuIr/C composite were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Although the Au and Ir in the AuIr/C did not form alloy, it is clear that the introduction of Ir decreases the average Au particle size to 4.2nm compared to that in the Au/C (10.1nm). By systematical analysis on chemical state of metal surface via XPS and the electrochemical results, it was found that the Au surface for the Au/C can be activated by potential cycling from 0.12V to 1.72V, resulting in the increased surface roughness of Au, thus improving the ORR activity. By the same potential cycling, the Ir surface of the Ir/C was irreversibly oxidized, leading to degraded ORR activity but uninfluenced OER activity. For the AuIr/C, Ir protects Au against being oxidized due to the lower electronegativity of Ir. Combining the advantages of Au and Ir in catalyzing ORR and OER, the AuIr/C catalyst displays an enhanced catalytic activity to the ORR and a comparable OER activity. In the 50-cycle accelerated aging test for the ORR and OER, the AuIr/C displayed a satisfied stability, suggesting that the AuIr/C catalyst is a potential bifunctional catalyst for the oxygen electrode.

Nafion-membrane-based proton exchange fuel cells (PEMFCs) typically operate at below 100 °C. However, H3PO4-doped polybenzimidazole (PBI)-based PEMFCs can operate at 100–200 °C. This is advantageous because of accelerated reaction rates and enhanced tolerance to poisons such as CO and SO2, which can arise from reformed gas or the atmosphere. However, the strong adsorption of phosphoric anions on the Pt surface dramatically decreases the electrocatalytic activity. This study exploits the “third-body effect”, in which a small amount of organic molecules are pre-adsorbed on the Pt surface to inhibit the adsorption of phosphoric anions. Pre-adsorbate species inhibit the adsorption of phosphoric anions, but can also partially occlude active sites. Thus, the optimum pre-adsorbate coverage is studied by correlating the oxygen reduction reaction (ORR) activity of Pt with pre-adsorbate coverage on the Pt surface. The influence of the pre-adsorbate molecule length is investigated using the organic amines, butylamine, octylamine, and dodecylamine, in both 0.1 mol/L HClO4and 0.1 mol/L H3PO4. Such amines readily bond to the Pt surface. In aqueous HClO4electrolyte, the ORR activity of Pt decreases monotonically with increasing pre-adsorbate coverage. In aqueous H3PO4electrolyte, the ORR activity of Pt initially increases and then decreases with increasing pre-adsorbate coverage. The maximum ORR activity in H3PO4occurs at a pre-adsorbate coverage of around 20%. The effect of molecular length of the pre-adsorbate is negligible, but its coverage strongly affects the degree to which phosphoric anion adsorption is inhibited. Butylamine adsorbs to Pt at partial active sites, which decreases the electrochemically active surface area. Adsorbed butylamine may also modify the electronic structure of the Pt surface. The ORR activity in the phosphoric acid electrolyte remains relatively low, even when using the pre-adsorbate modified Pt/C catalysts. Further development of the catalyst and electrolyte is required before the commercialization of H3PO4-PBI-based PEMFCs can be realized.

Exploring non-precious metal catalysts for the oxygen reduction reaction (ORR) is essential for fuel cells and metal–air batteries. Herein, we report a Fe-N-C catalyst possessing a high specific surface area (1501 m2/g) and uniformly dispersed iron within a carbon matrix prepared viaa two-step pyrolysis process. The Fe-N-C catalyst exhibits excellent ORR activity in 0.1 mol/L NaOH electrolyte (onset potential, Eo= 1.08 V and half wave potential, E1/2= 0.88 V vs. reversible hydrogen electrode) and 0.1 mol/L HClO4electrolyte (Eo= 0.85 V and E1/2= 0.75 V vs. reversible hydrogen electrode). The direct methanol fuel cells employing Fe-N-C as the cathodic catalyst displayed promising performance with a maximum power density of 33 mW/cm2in alkaline media and 47 mW/cm2in acidic media. The detailed investigation on the composition–structure–performance relationship by X-ray diffraction, X-ray photoelectron spectroscopy and Mössbauer spectroscopy suggests that Fe-N4, together with graphitic-N and pyridinic-N are the active ORR components. The promising direct methanol fuel cell performance displayed by the Fe-N-C catalyst is related to the intrinsic high catalytic activity, and critically for this application, to the high methanol tolerance.

Three-dimensional nanoporous metals of highly porous structure and interconnected ligaments are attractive for electrochemical reactions. Herein, freestanding 3D nanoporous silver (np-Ag) is prepared by a facile electrochemical approach, i.e., first electro-oxidizing silver to silver halides followed by electro-reduction of the silver halides by controlling the potential applied to the electrode. The np-Ag displays 130 and 11.5 times enhancement in catalytic activity for the oxygen reduction reaction and the formaldehyde electro-oxidation reaction, respectively, relative to the flat polycrystalline silver, and even outperforms the commercial nano-Pt catalyst. Detailed experimental and theoretical studies discover that both the facilitated mass transportation in the 3D interconnected porous structures and the favored kinetics contribute to the superior electro-catalytic activity of np-Ag.

PtSnRu/C catalysts with different atomic ratios and metal loadings were prepared using a polyol process to improve the performance of direct ethanol fuel cells (DEFCs). The catalysts were characterized using transmission electron microscopy and X-ray photoelectron spectroscopy. The DEFC performance was evaluated using a single-cell test. The ethanol electro-oxidation process and anode products were analyzed using in situ Fourier-transform infrared spectroscopy (FTIRS), gas chromatography, and neutralization titration. The performance of the Pt2.6Sn1Ru0.4/C catalyst was better than those of the Pt3Sn1/C and Pt2Sn1Ru1/C catalysts. The carbon-supported Pt2.6Sn1Ru0.4catalyst with a 60 wt% metal loading gave a maximum power density of 121 mW/cm2at 90 °C. In situ FTIRS and anode product analysis indicated that ethanol was electro-oxidized to acetaldehyde, acetic acid, ethyl acetate, and CO2. The ethanol oxidation efficiency on the Pt2.6Sn1Ru0.4/C catalyst was higher than that on the Pt3Sn1/C catalyst. The activation energy of ethanol electro-oxidation at the anode and surface composition analysis indicated that interactions among the surface elements resulted in a lower apparent activation energy and greater ethanol electro-oxidation efficiency on the Pt2.6Sn1Ru0.4/C catalyst.

Two-dimensional materials based on ternary system of B, C and N are useful ranging from electric devices to catalysis. The bonding arrangement within these BCN nanosheets largely determines their electronic structure and thus chemical and (or) physical properties, yet it remains a challenge to manipulate their bond structures in a convenient and controlled manner. Recently, we developed a synthetic protocol for the synthesis of crumpled BCN nanosheets with tunable B and N bond structure using urea, boric acid and polyethylene glycol (PEG) as precursors. By carefully selecting the synthesis condition, we can tune the structure of BCN sheets from s-BCN with B and N bond together to h-BCN with B and N homogenously dispersed in BCN sheets. Detailed experiments suggest that the final bond structure of B and N in graphene depends on the preferentially doped N structure in BCN nanosheets. When N substituted the in-plane carbon atom with all its electrons configured into the π electron system of graphene, it facilitates the formation of h-BCN with B and N in separated state. On the contrary, when nitrogen substituted the edge-plane carbon with the nitrogen dopant surrounded with the lone electron pairs, it benefits for the formation of B–N structure. Specially, the compound riched with h-BCN shows excellent ORR performance in alkaline solution due to the synergistic effect between B and N, while s-BCN dominant BCN shows graphite-like activity for ORR, suggesting the intrinsic properties differences of BCN nanosheets with different dopants bond arrangement.

Carbon supported Pt–Ni nanoparticles (NPs) electrocatalysts with nominal Pt/Ni atomic ratios of 3:1, 2:1, and 1:1, denoted as Pt3Ni/C, Pt2Ni/C, and Pt1Ni/C, respectively, were obtained by a modified polyol process. The structure of PtnNi/C (n= 3, 2, 1) electrocatalysts was studied by using an X-ray absorption spectroscopy technique combined with X-ray diffraction and transmission electron microscopy. Significantly, the NPs of Pt3Ni/C in air are demonstrated to have a quasi core–shell structure consisting of a core of metallic Pt surrounded by many small NiOxclusters. In contrast, both Pt2Ni/C and Pt1Ni/C are demonstrated to have an alloy structure with partial oxidation on the surface. Under the atmosphere of H2at 393 K, the PtnNi/C became the expected bimetallic alloy. At last, we discuss the effect of Ni amount on the structure of PtnNi/C and estimate their possible catalytic activity for methanol oxidation reaction. Our results further confirmed that the structure of Pt–Ni NPs can be influenced by Ni amount and this effect may be enlarged by environment effects.

Highly ordered polypyrrole nanowire arrays are constructed viaelectrochemically polymerizing pyrrole directly on Pd-modified Nafion® membrane. A significant enhancement in the performance and durability of direct methanol fuel cells (DMFCs) is observed when such an ordered structure is used as an ordered electrode.

Edle Ziele: Neue Nichtedelmetallkatalysatoren ermöglichen preiswerte H2‐Brennstoffzellen mit einer Leistung nahe der von Pt‐basierten Systemen. So wurde mithilfe eines Gerüsts aus zeolithischem ZnII‐Imidazolat als Umgebung für Fe‐ und N‐Ausgangsmaterialien ein Katalysator mit der bislang höchsten Leistung für Nicht‐Pt‐Katalysatoren hergestellt (Diagramm: volumetrische Stromdichte der besten Nicht‐Pt‐Katalysatoren und Zielwerte des U.S. DOE bei 0.8 V).

Carbon-supported bimetallic PtmNinelectrocatalysts with different Pt/Ni atomic ratios were synthesized through a modified polyol process. The as-prepared electrocatalysts were characterized by X-ray diffraction, transmission electron microscopy, voltammetry techniques, and single-cell tests. It was revealed that the PtmNinbimetallic nanoparticles were uniformly distributed on carbon supports with average diameters of about 3 nm. Pt and Ni were partially alloyed, indicated by the decreased Pt lattice constants compared with that of pure Pt. The results of the electrochemical measurements showed that the PtmNin/C catalysts, compared with the Pt/C, have superior specific activity toward the methanol electrooxidation reaction (MOR) in alkaline media as well as a higher power density in a direct methanol fuel cell test with the Pt3Ni1/C as the anode catalyst. Density functional theory studies further revealed that the electronic structure of Pt was modified by Ni due to the charge transfer from Ni to Pt atoms in PtmNinclusters, leading to a weakened CO adsorption on PtmNinbinary clusters than on Pt itself. This provides an explanation for the enhanced MOR activity of the PtmNin/C catalysts.

Two carbon-supported molybdenum nitrides, MoN/C and Mo2N/C, were prepared by varying the experimental conditions in NH3atmosphere. The physical properties of the catalysts were characterized by X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The catalytic activities of the catalysts toward the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) were characterized by potentiodynamic measurements. The results show that the MoN/C exhibits higher catalytic activity toward the ORR than the Mo2N/C. Both catalysts are inert to methanol. The results from the density functional theory calculation indicate that both the MoN and the Mo2N facilitate dissociation of oxygen molecules. The suitable geometric structure of the MoN and the preferred oxygen adsorption type on it contribute to the higher activity of the MoN/C toward the ORR. The calculation results agree well with the results from the experiments.

Double-walled carbon nanotubes (DWCNTs) with a large specific surface area, good crystallization, and netlike structure were synthesized by chemical vapor deposition. The DWCNT-supported platinum catalyst was prepared by a modified polyol method and used as a cathode catalyst for the oxygen reduction reaction (ORR) in direct methanol fuel cells. The Pt/DWCNT catalyst was characterized by X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry, and a single cell test. The TEM images showed that platinum particles with an average size of 2[?]3 nm were uniformly distributed on the surface of the DWCNTs when the platinum loading is as high as 60 wt %. The Pt binding energy of XPS showed a stronger interaction between Pt particles and DWCNTs than between Pt particles and Vulcan XC72R, and the Pt/DWCNT catalyst exhibited better activity and stability toward ORR than a commercial Pt/XC72R catalyst under identical conditions. This can be attributed to the unique properties of the DWCNTs, which can facilitate electron transfer, water removal, and oxygen access to the catalyst active sites.

Double-walled carbon nanotubes (DWNTs) supported platinum catalyst exhibited good activity and stability for oxygen reduction reaction (ORR). This can be attributed to its high specific surface area, relatively high crystallization and special network which can facilitate electron transfer, water removal and oxygen or air access to the catalyst active sites. The pore size distribution profile of DWNTs showed it had large part of mesopores which is favorable for mass transportation, X-ray diffraction patterns indicated that DWNTs is better in crystallization than the most used commercial carbon black XC72R. Platinum particles were uniformly distributed on the surface of DWNTs and its average size was 2~3 nm even for the nominal 60 wt% Pt/DWNTs catalyst. The actual Pt loading was 54.9 wt% calculated by scanning electron microscopy coupled with element dispersive spectroscopy (SEM-EDS) result for this 60 wt% Pt/DWNTs catalyst. Pt/DWNTs catalyst demonstrated better oxygen reduction activity and single-cell performance than commercial Pt/XC72R catalyst (from Johnson Matthey company) under identical conditions, and the single-cell performance was quite stable when it was discharged at constant current of 100 mA/cm2 for 20 hours.

Herein, the objective is to investigate the activation mechanism and activation process in high‐temperature proton exchange membrane fuel cell under different activation procedures from multiple perspectives. The effects of galvanostatic, temperature cycling, current step cycling, and increasing back pressure on cell performance were investigated by current density distribution test, electrochemical impedance spectroscopy, and distribution of relaxation times analysis. The results show that galvanostatic activation was the optimal activation mode. Current step cycling and elevating back pressure activation increase the voltage growth rate, but make the difference in the optimization of each parameter become greater, and do harm to cell performance stability and long‐term durability. Temperature cycling activation increases the charge transfer resistance and makes the uniformity of current density distribution deteriorate due to the thermal and mechanical stresses. It emphasizes the fact that different activation modes had great influence on the uniformity of current density distribution, and the optimization speed and change trend of each key parameter are not synchronized during the activation process. It is insufficient to focus only on voltage reaching steady state, and factors such as voltage, impedance, and uniformity of current density distribution should be considered comprehensively. Different activation modes have great influence on the uniformity of the current density distribution in a high‐temperature proton exchange membrane fuel cell, and the optimization speed and change trend of each key parameter are not synchronized during the activation process. It is insufficient to focus only on voltage reaching steady state, and factors such as voltage, impedance, and uniformity of current density distribution should be considered comprehensively.

Pt and PtRu nanoparticles supported on Vulcan XC-72R carbon obtained under different atmospheres (air and N2) were prepared via a polyol process in ethylene glycol solution and denoted as Pt/C−N2, Pt/C−air, PtRu/C−N2, and PtRu/C−air, respectively. The catalysts were characterized by XRD (X-ray diffraction), TEM (transmission electron microscopy), and XPS (X-ray photoelectron spectroscopy). TEM images show that metal nanoparticles are uniform in size and are well dispersed on the carbon support for all the catalysts. The mean particle sizes of Pt/C−N2, Pt/C−air, PtRu/N2, and PtRu/C−air are 2.6, 2.7, 2.3, and 1.8 nm, respectively. Among these samples, PtRu/C−air catalyst has the smallest nanoparticle size with a narrow size distribution. The three strongest diffraction peaks of both Pt/C−N2and Pt/C−air catalysts are located at 2 39°, 46°, and 67°, corresponding to the Miller indices of (111), (200), and (220) of a Pt fcc (face-centered cubic) crystal structure. The XRD pattern of PtRu/C−N2displays an fcc structure similar to that of Pt but different from that of PtRu/C−air. XPS analyses indicate that the amount of metallic Pt(0) and Ru(0) species present in Pt/C−N2and PtRu/C−N2catalysts are higher than those obtained in air atmosphere. Electrochemical voltammetry methods and single cell tests were employed to evaluate the activities of these catalysts. The results show that Pt/C−N2and PtRu/C−N2catalysts exhibit much better activities for oxygen reduction and methanol oxidation reactions in direct methanol fuel cells than the corresponding Pt/C−air and PtRu/C−air catalysts.

PtSnIr/C catalyst with a nominal atomic Pt/Sn/Ir ratio of 3: 1: 0.5 and Pt loading of 20 wt. % was synthesized with NaBH4 as a reducing agent. In comparison with Pt3Sn/C catalyst with the same nominal Pt loading, catalysts were characterized using X-ray diffraction (XRD), cyclic voltammetry (CV) and chrono-amperometry methods and single-cell tests. Pt3SnIr0.5/C catalyst showed enhanced electro-catalytic activity towards ethanol oxidation and better cell performance.

ORR (Oxygen Reduction Reaction) has been studied on Pt−Pd/C catalyst both experimentally and theoretically to gain insight into the promotion effect of PtPd nanoclusters to ORR and to provide guidelines for the design of an improved ORR catalyst. First, Pt3Pd1/C, Pt1Pd1/C, and Pt/C catalysts were prepared by the polyol process in ethylene glycol solution and characterized by XRD (X-ray diffraction), TEM (transmission electron microscope), and CV (cyclic voltammetry) techniques. XRD patterns reveal that all the catalysts have disordered face-centered cubic structures similar to the commercial Pt/C catalyst. Low-resolution TEM images indicate that the dispersion of the metal nanoparticles on the carbon support is uniform and in a narrow particle size range for Pt3Pd1/C and Pt/C catalysts, while for Pt1Pd1/C catalyst, the dispersion of the metal nanoparticles on the carbon support is uneven with a little agglomeration. Point resolved EDS (energy dispersive X-ray spectroscopy) of the individual particles have shown that both Pt and Pd are represented in the single nanoparticle for the Pt−Pd/C catalysts. CV tests show that Pd-containing catalysts of Pt3Pd1/C and Pt1Pd1/C have different features in the hydrogen adsorption−desorption region from pure Pt/C catalyst. The catalytic activity of Pt3Pd1/C for ORR is a little improved compared with Pt/C or Pt1Pd1/C catalyst in RDE (rotating disk electrode) measurement. Detailed work reveals that the activity of ORR could be further improved on Pt−Pd/C catalyst with Pt rich on the metal nanoparticles surface. This point is consistent with the theoretical calculation results. DFT (Density Function Theory) studies on the adsorption and dissociation of O2on Pt−Pd cluster indicate that the presence of Pd atoms facilitates the dissociation of O2on Pt sites.

An improved aqueous impregnation method was used to prepare 40 wt PtC electrocatalysts. TEM analysis of the samples showed that the Pt particles impregnated for a short time have a very narrow size distribution in the range of 1–4 nm with an average size of 2.6 nm. UV-vis spectroscopy measurements verified that the redox reaction between PtCl62−and formaldehyde took place with a slow rate at ambient temperature viaa two-step reaction path, where PtCl42−serves as an intermediate. The use of the short-time-impregnated 40 wt PtC as cathode electrocatalysts in direct methanol fuel cells yields better performance than that of commercial 40 wt PtC electrocatalyst. Experimental evidence provides clues for the fundamental understanding of elementary steps of the redox reactions, which helps in guiding the design and preparation of highly dispersed Pt catalyst for fuel cells.

A 75 h life test of a direct methanol fuel cell DMFC at a low current density of 100 mA cm−2was carried out. Electrochemical impedance spectroscopy EIS, scanning electron microscopy SEM and transmission electron microscopy TEM were applied to characterize the membrane electrode assembly MEA during the life test. The EIS results showed that the high frequency cell impedance of the MEA increased from 0.26 ohm cm2at the beginning of the life test to 0.37 ohm cm2at the end. SEM images of the MEA in cross-section apparently demonstrated the delamination of the electrodes from the membrane after the life test. TEM analysis of the electrocatalysts in the pre- and post-test cell revealed that the agglomeration of the metal particles in the anode was more serious than in the cathode. The results indicate that the agglomeration of electrocatalysts together with the delamination of the MEA concurrently contribute to the performance degradation of the DMFC.

An improved aqueous impregnation method was used to prepare 40 wt% Pt/C electrocatalysts. TEM analysis of the samples showed that the Pt particles impregnated for a short time have a very narrow size distribution in the range of 1–4 nm with an average size of 2.6 nm. UV-vis spectroscopy measurements verified that the redox reaction between PtCl₆2− and formaldehyde took place with a slow rate at ambient temperature via a two-step reaction path, where PtCl₄2− serves as an intermediate. The use of the short-time-impregnated 40 wt% Pt/C as cathode electrocatalysts in direct methanol fuel cells yields better performance than that of commercial 40 wt% Pt/C electrocatalyst. Experimental evidence provides clues for the fundamental understanding of elementary steps of the redox reactions, which helps in guiding the design and preparation of highly dispersed Pt catalyst for fuel cells.

Langmuir-Blodgett (LB) monolayers of three kinds of soluble polyimides were prepared with the direct deposition method. The monolayer structures were characterized with UV-vis absorption spectroscopy, the wide angle X-ray scattering method and electrochemical techniques. The polyimide molecules in the LB monolayers lie orderly on the substrate surfaces with the orientation in which the dianhydride group is normal to the substrate surface and two carbonyl oxygen groups close to the surface. Therefore, the thickness of the three kinds of polyimide LB monolayers are the same because it depends on the distance between the two carbonyl oxygen groups in the same ring. The area of monomeric units are dependent on the length of the diamine group. The model of the molecular packing proposed from the quantomechanical calculation is in good agreement with the experimental results.

The synchronous fluorescence spectra of hemoglobin solutions are reported for the first time. The main fluorescence peaks observed in the spectra are assigned. The effect of the concentration of hemoglobin solution on the spectra is studied. Characteristic fluorescence peaks due to the dimer and tetramer of hemoglobin molecules are recognized.

Fe–N–C catalysts are promising candidates to replace expensive and scarce Pt-based catalysts for oxygen reduction reaction (ORR) in fuel cell devices. Herein, simultaneous improvement of activity and stability of Fe–N–C is achieved through exposing active sites via a surface modification strategy. Concretely, EDTAFe groups are anchored on the external surface of zeolitic imidazolate framework-8 (ZIF-8) through size limitation, followed by pyrolysis to obtain ZIF@EDTAFe-1%-950, whose surface active site density increases more than 1.7 times as detected by X-ray photoelectron spectroscopy (XPS) and 57Fe Mössbauer spectra. Consequently, 1.7 times improvement of active site utilization efficiency in electrochemical measurements and more than 2 times performance enhancement in direct methanol fuel cells (DMFCs) are achieved due to facilitated mass transport as revealed by oxygen gain voltage and electrochemical impedance spectroscopy (EIS). Furthermore, through engineering robust drainage channels around exposed active sites to alleviate flooding, the assembled DMFC exhibits better stability than that of Pt/C in the first 3 h and remains 83.9% voltage after 24 h at 100 mA cm–2.

Within reach: Newly developed nonprecious‐metal catalysts can be used to produce inexpensive hydrogen fuel cells with performances approaching those of platinum‐based systems. For example, the best non‐Pt catalyst was prepared from a metal–organic framework consisting of zeolitic ZnIIimidazolate which served as the host for the Fe and N precursors of the catalyst. The plot shows the volumetric current densities of the best non‐Pt catalysts and the target value set by the U.S. DOE at 0.8 V).