3-Methyltrimethylammonium poly(2,6-dimethyl-1,4-phenylene oxide) based anion exchange membrane for alkaline polymer electrolyte fuel cells

Hydroxyl ion (OH^?) conducting anion exchange membranes based on modified poly (phenylene oxide) are fabricated for their application in alkaline polymer electrolyte fuel cells (APEFCs). In the present study, chloromethylation of poly(phenylene oxide) (PPO) is performed by aryl substitution rather than benzyl substitution and homogeneously quaternized to form an anion exchange membrane (AEM). ¹H NMR and FT-IR studies reveal successful incorporation of the above groups in the polymer backbone. The membrane is characterized for its ion exchange capacity and water uptake. The membrane formed by these processes show good ionic conductivity and when used in fuel cell exhibited an enhanced performance in comparison with the state-of-the-art commercial AHA membrane. A peak power density of 111 mW/cm² at a load current density of 250 mA/cm² is obtained for PPO based membrane in APEFCs at 30 °C.     

IrPd Nanoalloy-Structured Bifunctional Electrocatalyst for Efficient and pH-Universal Water Splitting

The lack of high efficiency and pH-universal bifunctional electrocatalysts for water splitting to hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) hinders the large-scale production of green hydrogen. Here, an IrPd electrocatalyst supported on ketjenblack that exhibits outstanding bifunctional performance for both HER and OER at wide pH conditions is presented. The optimized IrPd catalyst exhibits a specific activity of 4.46 and 3.98 A mg_Ir⁻¹ in the overpotential of 100 and 370 mV for HER and OER, respectively, in alkaline conditions. When applied to the anion exchange membrane electrolyzer, the Ir₄₄Pd₅₆/KB catalyst shows a stability of >20 h at a current of 250 mA cm⁻² for water decomposition, indicating promising prospects for practical applications. Beyond offering an advanced electrocatalyst, this work also guides the rational design of desirable bifunctional electrocatalysts for HER and OER by regulating the microenvironments and electronic structures of metal catalytic sites for diverse catalysis.     

Long-term performance of polyetheretherketone-based polymer electrolyte membrane in fuel cells at 95 °C

A poly(styrenesulfonic acid)-grafted polyetheretherketone (ssPEEK) polymer electrolyte membrane was developed by radiation grafting of ethyl styrenesulfonate (ETSS) onto PEEK film and subsequent hydrolysis. The long-term durability of the ssPEEK electrolyte membrane was tested in a fuel cell at 95 °C, during which it exhibited a lifetime of more than 1000 h and a slow voltage degradation of 18 μV h⁻¹ at a current density of 0.3 A cm⁻². After durability test, the catalyst layers were analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM); the polymer electrolyte membrane was investigated by determining the change in thickness, proton conductivity, and amounts of sulfonic acid groups. It was concluded that the degradation of performance in fuel cell was due to the thermal aging of the hydrocarbon polymer electrolyte membrane being exposed to the electrochemical environment with the pure oxygen acting as the oxidant gas, as well as the Nafion-based catalyst layer being subjected to high temperature for a long time, where the Pt catalyst was aggregated and sintered.     

质子交换膜燃料电池中碳纳米管负载的氧电极材料制备与表征

本文介绍了碳纳米管(CNTs)在质子交换膜燃料电池催化剂中的应用,对Pt/CNTs及Pt/C催化剂的比表面积、孔径、孔分布及金属表面分散情况进行了比较.实验发现,具备典型中孔结构的CNTs使得铂金属在其表面分散更加均匀.在催化剂制备工艺的研究中发现,合适的硝酸(40%)处理会使催化剂载体具备更加适宜的孔结构.通过本文的讨论,可以认为Pt/CNTs是一种可以应用在质子交换膜燃料电池上很有前景的电催化剂.     

Stability of the dry proton conductor CsHSO4 in hydrogen atmosphere

With an objective to assess the suitability of the dry proton conductor cesium hydrogen sulfate (CsHSO₄) as an electrolyte for fuel cells, its chemical stability in H₂ atmosphere in presence of the electrocatalyst Pt/C has been investigated. X-ray diffraction and differential scanning calorimetric (DSC) data indicate that CsHSO₄ decomposes to Cs₂SO₄ and H₂S at 150 °C in H₂ atmosphere when it is mixed with Pt/C catalyst, while it is quite stable under identical conditions in the absence of the Pt/C catalyst. Although thin composite membranes (∼80 μm) prepared with poly(vinylidene fluoride) and CsHSO₄ exhibit high proton conductivity at 150-200 °C that is adequate for fuel cell applications, development of compatible non-platinum alloy or transition metal oxide catalysts is needed before CsHSO₄ could be considered as an electrolyte for fuel cells. Also, processing procedures need to be optimized to obtain dense, gas impermeable membranes suitable for fuel cell applications.     

Hydroxyapatite-Derived Heterogeneous Ru-Ru2P Electrocatalyst and Environmentally-Friendly Membrane Electrode toward Efficient Alkaline Electrolyzer

Alkaline membrane water electrolysis is a promising production technology, and advanced electrocatalyst and membrane electrode design have always been the core technology. Herein, an ion-exchange method and an environmentally friendly in situ green phosphating strategy are successively employed to fabricate Ru-Ru₂P heterogeneous nanoparticles by using hydroxyapatite (HAP) as a phosphorus source, which is an exceptionally active electrocatalyst for hydrogen evolution reaction (HER). Density functional theory calculation results reveal that strong electronic redistribution occurs at the heterointerface of Ru-Ru₂P, which modulates the electronic structure to achieve an optimized hydrogen adsorption strength. The obtained Ru-Ru₂P possesses excellent HER performance (24 mV at 10 mA cm⁻²) and robust stability (1000 mA cm⁻² for 120 h) in alkaline media. Furthermore, an environmentally friendly membrane electrode with a sandwich structure is assembled by HAP nanowires as an alkaline membrane, Ru-Ru₂P as a cathodic catalyst, and NiFe-LDH as an anodic catalyst, respectively. The voltage of (−) Ru-Ru₂P || NiFe-LDH/CNTs (+) (1.53 V at 10 mA cm⁻²) is lower than that of (−) 20 wt% Pt/C || RuO₂ (+) (1.60 V at 10 mA cm⁻²) for overall water splitting. Overall, the studies not only design an efficient catalyst but also provide a new route to achieve a high-stability electrolyzer for industrial H₂ production.     

一种新型含氟含芴聚芳醚酮质子交换膜的合成和表征

以双酚芴、十氟联苯和磺化二氟酮为单体,合成磺化含氟聚芴醚酮(Sulfonated-fluo-rinated fluorene-containing poly(arylene ether ketone)s,SFPEEK).SFPEEK可溶于极性有机溶剂,具有较高的黏度,易于浇铸形成柔韧透明的薄膜.用其制成的质子交换膜表现出良好的热稳定性和抗水解、抗氧化性能.在相同测试条件下,SFPEEK膜具有与杜邦公司Nation 117膜相当的质子电导率,同时,具有比Nafion 117更好的耐甲醇渗透性能.直接甲醇燃料电池(DMFC)单池测试表明,放电到0.2 V时,用SFPEEK膜制备的单池电流密度可达66 mA/cm2,电池性能优于相同条件下用Nafion117膜组装的单池(电流密度60 mA/cm2).     

High Density Single Fe Atoms on Mesoporous N-Doped Carbons: Noble Metal-Free Electrocatalysts for Oxygen Reduction Reaction in Acidic and Alkaline Media

It remains a challenge to develop efficient noble metal-free electrocatalysts for the oxygen reduction reaction (ORR) in various renewable energy systems. Single atom catalysts have recently drawn great attention as promising candidates both due to their high activity and their utmost atom utilization for electrocatalytic ORR. Herein, the synthesis of an efficient ORR electrocatalyst that is composed of N-doped mesoporous carbon and a high density (4.05 wt%) of single Fe atoms via pyrolysis Fe-conjugated polymer is reported. Benefiting from the abundant atomic Fe–N₄ sites on its conductive, mesoporous carbon structures, this material exhibits an excellent electrocatalytic activity for ORR, with positive onset potentials of 0.93 and 0.98 V in acidic and alkaline media, respectively. Its electrocatalytic performance for ORR is also comparable to that of Pt/C (20 wt%) in both media. Furthermore, it electrocatalyzes the reaction almost fully to H₂O (or barely to H₂O₂). Additionally, it is durable and tolerates the methanol crossover reaction well. Furthermore, a proton exchange membrane fuel cell and a zinc–air battery assembled using it on their cathode deliver high maximum power densities (320 and 91 mW cm⁻², respectively). Density functional theory calculation reveals that the material's decent electrocatalytic performance for ORR is due to its atomically dispersed Fe–N₄ sites.     

Nitrogen-doped graphite encapsulated Fe/Fe_3C nanoparticles and carbon black for enhanced performance towards oxygen reduction

Non-noble metal(NNM) catalysts have recently attracted intensive interest for their high catalytic performance towards oxygen reduction reaction(ORR) at low cost.Herein,a novel NNM catalyst was synthesized by the simple pyrolysis of carbon black,urea and a Fe-containing precursor,which exhibits excellent ORR catalytic activity,superior durability and methanol tolerance versus the Pt/C catalyst in both alkaline and acidic solutions.Scanning electron microscopy(SEM),transmission electron microscopy(TEM) and X-ray diffraction(XRD) characterizations demonstrate that the product is a nitrogen-doped hybrid of graphite encapsulated Fe/Fe_3C nanoparticles and carbon black.X-ray photoelectron spectrum(XPS) and electrochemical analyses indicate that the catalytic performance and chemical stability correlate closely with a nitrogen-rich layer on the Fe/Fe_3C nanoparticle after pyrolysis with presence of urea,leading to the same four-electron pathway towards ORR as the Pt/C catalyst.The hybrid is prospective to be an efficient ORR electrocatalyst for direct methanol fuel cells with high catalytic performance at low cost.     

Nitrogen‐Induced Surface Area and Conductivity Modulation of Carbon Nanohorn and Its Function as an Efficient Metal‐Free Oxygen Reduction Electrocatalyst for Anion‐Exchange Membrane Fuel Cells

Nitrogen‐doped carbon morphologies have been proven to be better alternatives to Pt in polymer‐electrolyte membrane (PEM) fuel cells. However, efficient modulation of the active sites by the simultaneous escalation of the porosity and nitrogen doping, without affecting the intrinsic electrical conductivity, still remains to be solved. Here, a simple strategy is reported to solve this issue by treating single‐walled carbon nanohorn (SWCNH) with urea at 800 °C. The resulting nitrogen‐doped carbon nanohorn shows a high surface area of 1836 m² g^?1 along with an increased electron conductivity, which are the pre‐requisites of an electrocatalyst. The nitrogen‐doped nanohorn annealed at 800 °C (N‐800) also shows a high oxygen reduction activity (ORR). Because of the high weight percentage of pyridinic nitrogen coordination in N‐800, the present catalyst shows a clear 4‐electron reduction pathway at only 50 mV overpotential and 16 mV negative shift in the half‐wave potential for ORR compared to Pt/C along with a high fuel selectivity and electrochemical stability. More importantly, a membrane electrode assembly (MEA) based on N‐800 provides a maximum power density of 30 mW cm^?2 under anion‐exchange membrane fuel cell (AEMFC) testing conditions. Thus, with its remarkable set of physical and electrochemical properties, this material has the potential to perform as an efficient Pt‐free electrode for AEMFCs.     

Defect-Engineered ZIF-Derived Non-Pt Cathode Catalyst at 1.5 mg cm−2 Loading for Proton Exchange Membrane Fuel Cells

Due to the sluggish kinetics of the oxygen reduction reaction (ORR) by non-Pt based catalyst, high loading of catalyst is required to achieve satisfactory fuel cell performance, which inevitably leads to the increase of the catalyst layer thickness with serious mass transport resistance. Herein, a defective zeolitic imidazolate framework (ZIF) derived Co/Fe-N-C catalyst with small mesopores (2–4 nm) and high density of CoFe atomic active sites are prepared by regulating the Fe dosage and pyrolysis temperature. Molecular dynamics simulation and electrochemical tests indicate that > 2 nm mesopores show insignificant influence on the diffusion process of O₂ and H₂O molecules, leading to the high utilization of active sites and low mass transport resistance. The proton exchange membrane fuel cell (PEMFC) shows a high-power density of 755 mW cm⁻² with only 1.5 mg cm⁻² of non-Pt catalyst in the cathode. No apparent performance loss caused by concentration difference can be observed, in particular in the high current density region (1 A cm⁻²). This work emphasizes the importance of small mesopore design in the Co/Fe-N-C catalyst, which is anticipated to provide essential guidance for the application of non-Pt catalysts.     

Development of silver-gas diffusion electrodes for the oxygen reduction reaction by electrodeposition

Silver-gas diffusion electrodes (Ag-GDE) were prepared by direct deposition of the catalyst onto a carbon paper support by electrodeposition. This deposition technique, under potentiostatic and galvanostatic mode, allows the production of well dispersed ultra-low Ag loading levels. The catalytic activity of the prepared materials towards the oxygen reduction reaction (ORR) was investigated in the alkaline solution and its tolerance to methanol was evaluated. Based on an Ag-ink prepared from the electrodeposit material and RDE experiments, it was concluded that the ORR occurs via a four-electron pathway on the Ag electrodeposit. The combination of reasonably high catalytic activity, efficiency, low price, facile and green synthesis makes the electrodeposited Ag-GDE attractive for the ORR in alkaline fuel cells.     

Use of single wall carbon nanohorns in polymeric electrolyte fuel cells

Single wall carbon nanohorns (SWNH), produced by AC arc discharge in air, were used as Pt and PtRu supports in polymer electrolyte membrane fuel cells (PEMFC). These electrocatalysts were compared with equivalent electrocatalysts supported on commercial carbon back. The SWNH were characterized by differential thermal analysis (DTA), TEM, SEM, and XRD. The produced SWNH were 84.5 wt% pure, containing 3 wt% of amorphous carbon and 12.5 wt% of graphitic carbon. SWNH were used as electrocatalyst supports and tested in the electrodes of two types of polymer electrolyte fuel cells: H₂-fed PEMFC and direct methanol fuel cells (DMFC). The electrocatalyst nanoparticles anchored on both carbon supports were ca. 2.5 nm in diameter obtained by employing ethylene glycol as the reducing agent. The use of SWNH showed catalytic activities 60% higher than using carbon black as the electrocatalyst support in both types of fuel cells.     

铂钴合金纳米电催化剂的制备及性能研究

研制高活性的电催化剂是实现质子交换膜燃料电池的商业化应用必须解决的关键技术之一。本研究以三乙胺为碱性络合剂、硼氢化钠为还原剂, 采用液相合成法制备PtCo纳米合金电催化剂, 再通过高温热处理实现最佳电化学性能。采用各种表征方法对催化剂的微观结构及电化学性能进行测定, 探究硼氢化钠、三乙胺的添加量及高温热处理对催化剂电化学性能的影响。结果显示, 适量的硼氢化钠可提升催化剂的电化学活性面积, 三乙胺可以改变催化剂的质量活性, 高温热处理能有效提升催化剂的质量活性, 极大提升催化剂的氧还原反应(ORR)能力; 在同一测试体系下, 添加100 mg硼氢化钠及100 μL三乙胺在500 ℃高温热处理条件下制备的PtCo纳米合金电催化剂的质量活性达到133 mA/mg_Pt, 是田中贵金属工业株式会社(TKK)商用PtCo合金催化剂的3倍。     

Deposition of platinum nanoparticles on carbon nanotubes by supercritical fluid method

Carbon nanotube-supported platinum nanoparticles with a 5-15 nm diameter size range can be synthesized by hydrogen reduction of platinum(ll) acetylacetonate in methanol modified supercritical carbon dioxide. X-ray photoelectron spectroscopy and X-ray diffraction spectra indicate that the carbon nanotubes contain zero-valent platinum metal and high-resolution transmission electron microscopy images show that the visible lattice fringes of platinum nanoparticles are crystallites. Carbon nanotubes synthesized with 25% by weight of platinum nanoparticles exhibit a higher activity for hydrogenation of benzene compared with a commercial carbon black platinum catalyst. The carbon nanotube-supported platinum nanocatalyst can be reused at least six times for the hydrogenation reaction without losing activity. The carbon nanotube-supported platinum nanoparticles are also highly active for electrochemical oxidation of methanol and for reduction of oxygen suggesting their potential use as a new electrocatalyst for proton exchange membrane fuel cell applications.     

Electrical enhancement of DMFC by Pt-M/C catalyst-assisted PVD

Direct methanol fuel cells (DMFC) are studied extensively owing to their simple cell configuration, high volume energy density, short start-up time and operation reliability. However, the major drawbacks include high production cost, catalyst and methanol crossover poisoning. This study presents a simple method for Pt-M/C catalyst preparation using a magnetron sputtering (MS) and metal-plasma ion implantation (MPII) technique. The Pt catalysts were sputtered onto a gas diffusion layer (GDL), followed by implanting Cr, Fe, Ni, and Mo catalysts using MPII (accelerating voltage is 20 kV and implantation fluence is 1 × 10¹⁶ ions/cm²). The crystallinity and microstructure of the catalyst films were analyzed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM). The cell performance was tested using potential stat/galvano station. The results indicate that the membrane electrode assembly for Pt-Ni/C, Pt-Fe/C and Pt-Cr/C catalysts can enhance DMFC cell performance, compared with traditional Pt/C and Pt-Ru/C. The maximum Pt-Ni/C power density is 2.4 mW/cm² with an open circuit voltage (OCV) 0.334 V when tested at a methanol concentration of 1 M.     

Cooperative Boron and Vanadium Doping of Nickel Phosphides for Hydrogen Evolution in Alkaline and Anion Exchange Membrane Water/Seawater Electrolyzers

Developing low-cost and high-performance transition metal-based electrocatalysts is crucial for realizing sustainable hydrogen evolution reaction (HER) in alkaline media. Here, a cooperative boron and vanadium co-doped nickel phosphide electrode (B, V-Ni₂P) is developed to regulate the intrinsic electronic configuration of Ni₂P and promote HER processes. Experimental and theoretical results reveal that V dopants in B, V-Ni₂P greatly facilitate the dissociation of water, and the synergistic effect of B and V dopants promotes the subsequent desorption of the adsorbed hydrogen intermediates. Benefiting from the cooperativity of both dopants, the B, V-Ni₂P electrocatalyst requires a low overpotential of 148 mV to attain a current density of −100 mA cm⁻² with excellent durability. The B, V-Ni₂P is applied as the cathode in both alkaline water electrolyzers (AWEs) and anion exchange membrane water electrolyzers (AEMWEs). Remarkably, the AEMWE delivers a stable performance to achieve 500 and 1000 mA cm⁻² current densities at a cell voltage of 1.78 and 1.92 V, respectively. Furthermore, the developed AWEs and AEMWEs also demonstrate excellent performance for overall seawater electrolysis.     

Atomically Dispersed Silver Atoms Embedded in NiCo Layer Double Hydroxide Boost Oxygen Evolution Reaction

Bimetallic layered double hydroxides (LDHs) are promising catalysts for anodic oxygen evolution reaction (OER) in alkaline media. Despite good stability, NiCo LDH displays an unsatisfactory OER activity relative to the most robust NiFe LDH and CoFe LDH. Herein, a novel NiCo LDH electrocatalyst modified with single-atom silver grown on carbon cloth (Ag_SA-NiCo LDH/CC) that exhibits exceptional OER activity and stability in 1.0 m KOH is reported. The Ag_SA-NiCo LDH/CC catalyst only requires a low overpotential of 192 mV to reach a current density of 10 mA cm⁻², obviously boosting the OER activity of NiCo LDH/CC (410 mV@10 mA cm⁻²). Inspiringly, Ag_SA-NiCo LDH/CC can maintain its high activity for up to 500 h at a large current density of 100 mA cm⁻², exceeding most single-atom OER catalysts. In situ Raman spectroscopy studies uncover that the in situ formed NiCoOOH during OER is the real active species. Hard X-ray absorption spectrum (XAS) and density functional theory (DFT) calculations validate that single-atom Ag occupying Ni site increases the chemical valence of Ni elements, and then weakens the adsorption of oxygen-contained intermediates on Ni sites, fundamentally accounting for the enhanced OER performance.     

阴离子交换膜燃料电池阳极催化剂的研究进展

阴离子交换膜燃料电池(AEMFC)可使用非贵金属催化剂,且电极反应速率快。阳极催化剂的选择和制备对提高燃料氧化速率和燃料电池的电流密度及降低成本等有很大影响。本文从阴离子交换膜阳极催化剂的种类、制备方法,催化剂的载体等角度对阳极催化剂的研究现状进行分析。分析表明,在阳极催化剂中掺杂金属、金属氧化物或非金属氧化物,能充分发挥各元素的协同作用,从而提高催化剂的电催化性能;改进制备方法可以提高催化剂的比表面积,改变元素的分布。对催化剂载体进行改性以改善载体自身的孔径分布,提高比表面积和稳定性,或寻求导电性好、比表面积大、耐腐蚀的新载体材料(如SiC、Ti等),均可以提高催化剂的载量和催化剂在载体上的分散度等,从而提高阴离子交换膜燃料电池的性能。     

ZTIFs derived nitrogen-introduced high specific area and hierarchical porous carbon for oxygen reduction reaction

It is of great allure to construct nitrogen-doped hierarchical porous carbon to replace Pt-based catalysts for efficient ORR. Here, nitrogen-doped hierarchical porous carbon (NHPC) was prepared by carbonizing ZTIF-1 and KOH activating. The resultant NHPC4-700 catalyst exhibits a hierarchical porous structure and high specific area (2404 m² g^?1), which promoted the exposure of enough active sites as well as simultaneously enhanced the electron transfer rate, shorten the mass transfer pathway, enhanced ionic conductivity and carbon wetting. The results are capable of remarkably improving the ORR activities of carbon materials. The NHPC4-700 catalyst exhibits a great catalytic performance with onset potential at 0.90 V and limiting current density of ??6.0 mA cm^?2, which is close to commercial Pt/C electrocatalyst. Meanwhile, the NHPC4-700 catalysts had better stability and methanol resistance than that of Pt/C toward ORR. These superior electrochemical properties of the NHPC4-700 catalysts were closely related to their nitrogen-doped hierarchical porous structure and high specific area.