Alkaline Fuel Cells Research Articles

Fuel Cell Technology Evolution: Insights into Polymer, Solid Oxide, and Alkaline Fuel Cells

Fuel Cell Technology Evolution: Insights into Polymer, Solid Oxide, and Alkaline Fuel Cells

Deep Eutectic Solvent Supported Polymer-Based High Performance Anion Exchange Membrane for Alkaline Fuel Cells

Alkaline anion exchange membrane fuel cells (AEMFC) have gained interest due to their potential as electrochemically energy conversion devices and a competitive alternative to the more extensively studied commercialized proton exchange membrane fuel cells (PEMFCs). Nevertheless, their development impedes the limited ion conductivity, chemical and mechanical stability in an alkaline medium of anion exchange membranes (AEMs). The ionic conductivity of AEM is lower than that of a proton exchange membrane (PEM) because the mobility of hydroxide ions is inherently lower than that of protons [1]. Deep eutectic solvents (DESs) as green solvents can overcome this issue.The main idea of this research is to fabricate a deep eutectic solvent-supported polymer-based AEM for alkaline fuel cell application by electrospinning technique. Poly(vinyl alcohol) (PVA) is one of the potential polymers for the development of AEM due to its water solubility, biodegradability, high fiber forming ability, non-toxicity, and high chemical and thermal stability [2]. This work aims to achieve high ionic conductivity, chemical and mechanical stability by two methods: swelling polyvinyl alcohol (PVA)-based nanofibers into DES and encapsulating DES inside the PVA-nanofibers together with optimizing fabrication methods.In this study, polymer electrolytes as potential AEMs were first prepared using the swelling method, where electrospun PVA nanofibers were fabricated via the electrospinning technique, followed by swelling in a series of DESs. To prepare the DES solutions, choline chloride (ChCl) and ethylene glycol (EG) were mixed at different molar ratios. The cross-linking of pure PVA fibers with glutaraldehyde in ethanol (see Figure 1B) and DES uptake and the presence of voids as channels for ion conduction (see Figure 1C) were successfully confirmed with a scanning electron microscopy (SEM, Crossbeam500, Zeiss). The ionic conductivity of swelled in DES PVA-based membranes were evaluated by electrochemical impedance spectroscopy (Metrohm Autolab) at room temperature and was equal to 0.336 mS/cm. The presence of DES in the membrane was confirmed with FTIR spectroscopy (FT-IR spectrometer, Nicolet iS10): a slight C-N+ peak at 953 cm-1 from ChCl has proven interaction between PVA and DES with FTIR spectroscopy, meaning that DES is present in the fiber. In addition, the nitrogen content in the obtained membrane was determined by CHNS elemental analysis (Elemental Vario micro cube) as 3.32 wt.%.In order to overcome high weight loss in the swelling method, the encapsulation method was suggested as an alternative option, which is based on the encapsulation of DES into the PVA solution by mixing them, varying the amount of DES added, and then preparing fibers using electrospinning. Observing the morphology of DES-encapsulated PVA nanofibers with a scanning electron microscope (SEM, Crossbeam500, Zeiss), as the content of DES in the solution increased, there was an observed rise in the average diameter of the nanofibers (see Figure 1D). Encapsulation of DES in PVA nanofibers was primarily confirmed by transmission electron microscope (TEM, JEM -1400 Plus, JEOL): PVA appears lighter due to its decreased density, proving that DES is present inside the fibers. Also, the same tendency was observed with the results of FTIR spectroscopy (FT-IR spectrometer, Nicolet iS10) as for the swelling method, meaning that DES is present in the fiber. According to CHNS elemental analysis (Elemental Vario micro cube), nitrogen content was lower than for the swelling method - 0.70 wt.%. The ionic conductivity was evaluated as 0.364 mS/cm by electrochemical impedance spectroscopy (Metrohm Autolab) at room temperature, which was almost the same as for the swelling method.As a result, very flexible and visually transparent electrospun DES-supported PVA-based AEMs were obtained via the swelling and encapsulation method.

Partially PEG-Grafted Poly(Terphenyl Piperidinium) Anion Exchange Membranes with Balanced Properties for Alkaline Fuel Cells.

Poly(ethylene glycol) (PEG) or oligo (ethylene glycol) (OEG) grafted anion exchange membranes (AEMs) exhibit improved ionic conductivity, high alkaline stability, and subsequent boosted AEM fuel cell performance, but too much PEG/OEG side chains may can result in a reduction in the ion exchange capacity (IEC), which can have adverse effects on ion transport. Here, a series of partially PEG-grafted poly(terphenyl piperidinium) with different side chain length are synthesized using simple postpolymerization modification to produce AEMs with balanced properties. The polar and flexible PEG side chains are responsible for the controlled water uptake and swelling, superior hydroxide conductivity (122 mS cm-1 at 80 °C with an IEC of 1.99mmol g-1), and enhanced alkaline stability compared to the reference sample without PEG grafts (PTP). More importantly, the performance of AEM fuel cell (AEMFC) with the membrane containing partial PEG side chains surpasses that with PTP membrane, demonstrating a highest peak power density of 1110mW cm-2 at 80 °C under optimized conditions. This work provides a novel approach to the fabrication of high-performance AEM materials with balanced properties for alkaline fuel cell application.

Phosphorus-Doping Enables the Superior Durability of a Palladium Electrocatalyst towards Alkaline Oxygen Reduction Reactions.

The sluggish kinetics of oxygen reduction reactions (ORRs) require considerable Pd in the cathode, hindering the widespread of alkaline fuel cells (AFCs). By alloying Pd with transition metals, the oxygen reduction reaction's catalytic properties can be substantially enhanced. Nevertheless, the utilization of Pd-transition metal alloys in fuel cells is significantly constrained by their inadequate long-term durability due to the propensity of transition metals to leach. In this study, a nonmetallic doping strategy was devised and implemented to produce a Pd catalyst doped with P that exhibited exceptional durability towards ORRs. Pd3P0.95 with an average size of 6.41 nm was synthesized by the heat-treatment phosphorization of Pd nanoparticles followed by acid etching. After P-doping, the size of the Pd nanoparticles increased from 5.37 nm to 6.41 nm, and the initial mass activity (MA) of Pd3P0.95/NC reached 0.175 A mgPd-1 at 0.9 V, slightly lower than that of Pd/C. However, after 40,000 cycles of accelerated durability testing, instead of decreasing, the MA of Pd3P0.95/NC increased by 6.3% while the MA loss of Pd/C was 38.3%. The durability was primarily ascribed to the electronic structure effect and the aggregation resistance of the Pd nanoparticles. This research also establishes a foundation for the development of Pd-based ORR catalysts and offers a direction for the future advancement of catalysts designed for practical applications in AFCs.

Fluorinated Poly(thiophene-based aryl piperidinium) Anion-Exchange Membranes Containing Dual Cation–Dipole Interactions for Alkaline Fuel Cells

Fluorinated Poly(thiophene-based aryl piperidinium) Anion-Exchange Membranes Containing Dual Cation–Dipole Interactions for Alkaline Fuel Cells

The Performance Evaluation of a Hybrid System Combining an Alkaline Fuel Cell with an Inhomogeneous Thermoelectric Generator

To harness the full potential of the exhaust heat produced by an alkaline fuel cell (AFC), a novel coupling system that combines an AFC with an inhomogeneous thermoelectric generator (ITEG) is proposed. Detailed models of both the AFC and ITEG are developed, accounting for various irreversible losses. Following model validations, mathematical expressions for the power output density (POD) and energy efficiency (EE) of the hybrid system are derived. Though performance comparisons, the hybrid system’s effectiveness and competitiveness are demonstrated. Our calculation results reveal that the hybrid system achieves a 31.19% increase in its maximum POD and 54.61% improvement in its corresponding EE compared to that of the standalone AFC. Furthermore, numerous parametric studies are conducted. Some findings indicate that the POD of the hybrid system can be improved by elevating the operating temperature of the AFC and the environmental temperature, and that it can be optimized using the geometric characteristics of an ITEG. However, the EE of the hybrid system gains improvement via increasing the operating temperature of the AFC or decreasing both the environmental temperature and geometric characteristics of the ITEG. Additionally, the coefficient of the spatial inhomogeneity of the ITEG determines the optimal operating current density of the AFC. These insights offer valuable guidance for the integration and operation of practical hybrid systems.

One‐Pot Synthesis of Carbon‐Supported Pd Nanoparticles with Ni and Carbon Matrix Protection for Durable Alkaline Hydrogen Oxidation Reaction

Protecting nanoparticles with a carbon matrix can enhance the durability of the catalysts in alkaline fuel cells (AFC) and is well‐documented. While others have tried complex syntheses to produce small nanoparticle catalysts, in this work, in order to scale‐up batches of 15 g or more, carbon‐cap (or carbon‐coating) protected Vulcan XC72‐supported Pd‐Ni (1‐2) nanoparticles (Pd‐Niacc/C) were successfully synthesized via a one‐step dry‐synthesis process. This catalyst was compared with a commercial Pd‐Ni/Vulcan XC72 material (PdNi/C, Premetek) in terms of hydrogen oxidation reaction (HOR) activity and stability. To produce less ordered carbon caps (versus graphite/graphene), a low‐temperature heat‐treatment (below 500°C) was used, resulting in Pd‐Niacc/C of unique electrochemical properties: easily electrochemically activated, this catalyst outperforms PdNi/C for alkaline HOR and proves more durable under highly oxidizing accelerated stress test (AST) conditions. Identical location transmission electron microscopy (ILTEM), X‐ray photoelectron spectroscopy (XPS) and rotating disk electrode (RDE) measurements demonstrate how the Ni‐rich surface plays an important role in HOR activity for both PdNi/C and PdNiacc/C and that the protective carbon‐coating of the latter ensures better durability of performance and better resistance to materials degradation.

A comprehensive review on different types of fuel cell and its applications

This review article provides an overview of various types of fuel cells that are currently being researched and developed. Fuel cells are electrochemical devices that convert chemical energy directly into electrical energy, making them a promising technology for clean and efficient energy production. The review covers the principles of operation and key characteristics of proton exchange membrane fuel cells (PEMFCs), solid oxide fuel cells (SOFCs), alkaline fuel cells (AFCs), direct methanol fuel cells (DMFCs), and microbial fuel cells (MFCs). The article also discusses the advantages and limitations of each type of fuel cell, as well as the current research and development efforts aimed at improving their performance and reducing their costs. Overall, this review provides a comprehensive understanding of the various types of fuel cells and their potential applications in the field of energy production.

Innovative use of air gap membrane distillation to harvest waste heat from alkaline fuel cell for efficient freshwater production: A comprehensive 4E study

Poor power density of alkaline fuel cell (AFC) resulting from inherent waste heat generation significantly hinders its widespread application. Herein, an innovative hybrid system that combines AFC and air gap membrane distillation is proposed, aiming to enhance the power density via utilizing the waste heat for freshwater generation. Based on the laws of thermodynamics and electrochemical theory, the hybrid system model is formulated to derive performance metrics by quantifying various irreversible losses. The thermodynamic performance, competitiveness, economic viability, and environmental impact of the system are comprehensively discussed through energetic, exergetic, economic, environmental (4E) analyses. Calculations predict that the maximum equivalent output power density permits 63.28% higher than that of the standalone AFC at 353 K. The influencing mechanisms of the AFC operation conditions, air gap thickness, and properties of the porous hydrophobic membrane are clarified to discern potential avenues for further performance improvement. Furthermore, a multi-objective local sensitivity analysis indicates that membrane porosity and coolant solution temperature are the most sensitive factors. The levelized costs study reveals that water and electricity costs over the total lifecycle are 56.89 $m−3 and 0.1012 $kWh−1, respectively. The multi-objective optimization further provides a high-performance and cost-effective design solution for the hybrid system.

Modeling, thermodynamic performance analysis, and parameter optimization of a hybrid power generation system coupling thermogalvanic cells with alkaline fuel cells

During the operation of alkaline fuel cells (AFCs), a significant amount of waste heat is generated, which has negative impacts on energy utilization and the environment. To improve energy efficiency, cost savings, environmental sustainability, and industrial practices, an effective approach is proposed to employ thermogalvanic cells (TGCs) for electric power generation by harvesting low-grade exhaust heat produced in AFCs. A mathematical model of the AFC-TGC hybrid system is established, taking into account the three overpotential losses in AFCs and the irreversible heat losses in TGCs. Based on this thermal-electric coupled model, we investigate the hybrid system’s output performance characteristics and optimal parameter design. The calculated results indicate that the hybrid system achieves a considerable increase of 19.72% in maximum power density from 247.07 W m−2 to 295.80 W m−2 and 5.71% in conversion efficiency from 10.16% to 10.74% compared to a single AFC, respectively. In addition, the output performance of the hybrid system can be further improved by adjusting system parameters such as the AFC’s operating temperature, the length of each TGC cell, the heat sink temperature, and the thermal convection coefficient. More importantly, a comparative study of the maximum power density of AFC-based cogeneration systems reveals that the TGC demonstrates a remarkable ability to economically recover waste heat from the AFC, surpassing previously reported thermal energy utilization devices. This study provides important theoretical guidance for the optimal design and parametric analysis of AFC-TGC hybrid systems, thereby facilitating the development of high-performance energy cascade utilization systems based on AFC devices.

Exploring the Potential of α-MnO<sub>2</sub>/ Carbon Nanotubes for Improved Oxygen Reduction Reaction Performance at the Cathode of Alkaline Fuel Cells

In the field of fuel cell technology, the development of cost-effective catalysts is crucial for the commercialization of Alkaline Membrane Fuel Cells (AMFCs). Platinum (Pt) has traditionally been employed as the catalyst in AMFCs, but its high cost poses a major barrier to widespread adoption. In this study, a new catalyst material was developed by incorporating Manganese Dioxide (α-MnO2) into Carbon Nanotubes (CNTs) using hydrothermal synthesis techniques. The synthesized catalyst was characterized using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD), and its electrocatalytic activity was evaluated through Linear Sweep Voltammetry (LSV) and CV through Rotating Disc Electrode (RDE) experiments. The results showed that the α-MnO2-CNT composite displayed strong durability in the alkaline environment and high electrocatalytic activity for oxygen reduction reaction (ORR). The LSV measurements revealed a current density of -4.1 mA/cm2 and an overpotential of -0.3V relative to Standard Calomel Electrode (SCE) in a 0.1M KOH electrolyte. Additionally, the α-MnO2-CNT composite displayed high methanol tolerance and long-term stability compared to commercial Pt/C catalysts. This study demonstrates that the use of α-MnO2-CNT as a cost-effective alternative to Pt has the potential to facilitate the commercialization of AMFC technology.

Synthesis and Characterization of Sorbitol Membraneless Alkaline Fuel Cell Catalysts for Cathode and Anode, Utilizing AgV2O5/C, AgMnO2/C, and PdCeO2/C Catalysts

This study aimed to develop sorbitol fuel cell catalysts for cathode and anode fuels by synthesizing AgV2O5/C, AgMnO2/C, and PdCeO2/C catalysts. The physical characteristics of the catalysts were analyzed using SEM and EDS. The results showed that the prepared catalysts were small, lumpy, and densely clustered on the carbon surface with small particles. The electrochemical characteristics of the oxidation of alkaline fuels using sorbitol as fuel were investigated by assessing sorbitol concentration ratios of 0.1, 0.2, 0.3, 0.4 and 0.5 per 0.1 M alkaline KOH solution through cyclic voltammetry. The PdCeO2/C catalyst at a concentration of 0.1 M sorbitol solution exhibits the highest potential difference at the potential range of -0.5 to 0.5 V, resulting in a maximum current density of 0.2 mA/cm2. The AgV2O5/C and AgMnO2/C catalysts were tested in the reduction reaction, and the concentration ratios of sorbitol solution per 0.1 M alkaline KOH solution varied from 0.1 to 0.5 M. The results demonstrated a decrease in activity in the catalyst reduction reaction as the sorbitol solution concentration increased, indicating a potential correlation with enhanced oxidation resistance. HIGHLIGHTS In order to achieve the highest efficiency and suitability in an electric cell, it is essential for the AgV2O5/C and AgMnO2/C catalysts to possess excellent resistance to cathode oxidation The AgV2O5/C and AgMnO2/C catalysts function as cathode-side catalysts involved in reduction reactions. Consequently, it is imperative for these catalysts to exhibit exceptional resistance to oxidation at the cathode At a concentration of 0.1 M KOH solution, the PdCeO2/C catalyst exhibited a maximum oxidation current density of 0.2 mA/cm² GRAPHICAL ABSTRACT

Highly Conducting and Stable Partial Fluorinated Polymer–Silica-Based Anion Exchange Membrane for Alkaline Fuel Cells

Highly Conducting and Stable Partial Fluorinated Polymer–Silica-Based Anion Exchange Membrane for Alkaline Fuel Cells

Atomically Dispersed Zn/Co-N-C as ORR Electrocatalysts for Alkaline Fuel Cells.

Hydrogen fuel cells have drawn increasing attention as one of the most promising next-generation power sources for future automotive transportation. Developing efficient, durable, and low-cost electrocatalysts, to accelerate the sluggish oxygen reduction reaction (ORR) kinetics, is urgently needed to advance fuel cell technologies. Herein, we report on metal-organic frameworks-derived nonprecious dual metal single-atom catalysts (SACs) (Zn/Co-N-C), consisting of Co-N4 and Zn-N4 local structures. These catalysts exhibited superior ORR activity with a half-wave potential (E1/2) of 0.938 V versus RHE (reversible hydrogen electrode) and robust stability (ΔE1/2 = -8.5 mV) after 50k electrochemical cycles. Moreover, this remarkable performance was validated under realistic fuel cell working conditions, achieving a record-high peak power density of ∼1 W cm-2 among the reported SACs for alkaline fuel cells. Operando X-ray absorption spectroscopy was conducted to identify the active sites and reveal catalytic mechanistic insights. The results indicated that the Co atom in the Co-N4 structure was the main catalytically active center, where one axial oxygenated species binds to form an Oads-Co-N4 moiety during the ORR. In addition, theoretical studies, based on a potential-dependent microkinetic model and core-level shift calculations, showed good agreement with the experimental results and provided insights into the bonding of oxygen species on Co-N4 centers during the ORR. This work provides a comprehensive mechanistic understanding of the active sites in the Zn/Co-N-C catalysts and will pave the way for the future design and advancement of high-performance single-site electrocatalysts for fuel cells and other energy applications.

A Recent Comprehensive Review of Fuel Cells: History, Types, and Applications

This review discusses the history, fundamentals, and applications of different fuel cell technologies, including proton exchange membrane fuel cells (PEMFCs), direct methanol fuel cells, solid oxide fuel cells (SOFCs), phosphoric acid fuel cells (PAFCs), alkaline fuel cells (AFCs), and molten carbonate fuel cells (MCFCs). Recent advances in fuel cell technologies have led to potential applications in aerospace, transportation, and portable and stationary power generation due to high efficiency and low emissions. Fuel cell types are also compared based on efficiency, operating temperature, lifetime, energy/power density, and cost. It was noticed that PEMFCs have the highest mass power density, reaching 1,000 W/kg compared to less than 100 W/kg for SOFCs, which makes them suitable for portable applications such as aircraft. PEMFCs and AFCs are suitable for low‐temperature applications and are highly efficient. SOFCs and MCFCs are better for high‐temperature operations. SOFCs are robust and suitable for high‐power demands, while MCFCs are advantageous for high‐power output. Hydrogen fuel cells promise to decarbonize transportation and aviation sectors with the advantages of lower weight, compactness, and quick startup times. However, challenges remain around renewable hydrogen production/infrastructure and aircraft integration, besides hydrogen storage, water management inside fuel cells, and operational robustness under varying pressures. Generally, for all fuel cell types, more focus should be given to enhancing the stability and efficiency of fuel cell materials and reducing their cost.

Structure and materials of alkaline fuel cell

To solve the problems of energy and environment, after experimentations and selections, hydrogen steps into the limelight; we call it "the ultimate energy source for the development of human society," and fuel cell technology is an essential step of pursuing the recyclable hydrogen energy. Fuel Cell is viewed as one of "The ideal power generation devices in the 21st century"; it has a high energy transformation efficiency, and the electricity generation process has a low environmental impact. If the fuel is being provided, fuel cells can continuously provide electricity, which can likely be applied in power plants, electric vehicles, electronic devices, mobile communications, and space facilities. This work focuses on Alkaline Fuel Cells. The oxidation-reduction process will be more straightforward in alkaline-based electrolytes than in acidic electrolytes, and the alkaline system will also perform better under room temperature. Besides, Alkaline Fuel Cells (AFC) can use non-platinum catalysts, so the cost is lower than the other Fuel Cells. Thus, designing a Hydrogen-based AFC is what's being focused on in this article. However, AFC has its disadvantages too. First, the CO2 in air and fuel gas must be cleaned up because of the alkaline electrolyte. Furthermore, water is a by-product of the electrochemical reactions inside AFCs. Therefore, AFC performance will be seriously affected if the water doesn`t expel. Another issue that current AFCs face is the problem of CO2 poisoning. To address the above questions, we approached it from a thermodynamic perspective, compared the basic structure, material, drainage method, etc., of multiple alkaline fuel cells, and selected the more efficient ones that will be more effective for developing the AFCs.

Advancing alkaline fuel-cells cathode through synergistic catalyst design: Integrated LDH-derived ternary mixed metal oxide with N/Co multi-doped reduced graphene oxide

The fabrication of efficient and affordable nanomaterials is the bottleneck in the advancement of energy conversion/storage technologies. This study presents the synthesis and performance assessment of a novel hybrid nanostructure comprising LDH-calcinated Ternary Mixed Metal Oxide (3MMO) nanoflakes, incorporated on multi-doped (Nitrogen and single atom cobalt) Reduced Graphene Oxide (CoNG), as a ptoficient electrocatalyst for Oxygen Reduction Reaction (ORR) in an alkaline environment. The synthesized nanocomposites underwent a comprehensive analysis and discussion, employing several physicochemical and electrochemical characterization methods. The physiochemical analyses collectively affirmed the successful incorporation of the 3MMO onto the CoNG lattice forming a mesoporous structure. In terms of electrochemical characterization, the 3MMO-CoNG nanocomposite displayed the most favorable electrochemical attributes, including an onset potential of −0.04 V vs. Ag/AgCl, an electron transfer number of 3.8, remarkable current retention (85 %) after an extended period of 18000 s, and the lowest charge transfer resistance (29 Ω) among the synthesized samples. The synergistic interaction between the 3MMO nanoparticles and the CoNG lattice contributes to the improved electrochemical performance of 3MMO-CoNG. The results of this investigation demonstrate that the developed catalyst displays exceptional electrochemical performance, rivaling the most effective catalysts documented in existing literature.

The Positive Effects of Carbon-Coating Layers on Protecting the Nanoparticle Towards Poisoning Ions or Gases

Recently, the research that explores the positive effects of carbon-coating nanoparticles to fight the severe oxidation/corrosion in Alkaline fuel cell (AFC), Proton-exchange membrane fuel cell (PEMFC) or water electrolyzer is well-recognized, since the carbon layers can extend the catalyst’s durability towards hydrogen oxidation/evolution reactions (HOR, HER) and oxygen evolution/reduction reactions (OER, ORR). Especially for the reactions in alkaline pH, with the graphite coating, the Ni nanoparticles in both HOR and HER can resist passivation and hydride poisoning. [1,2] Similarly, in the same alkaline conditions, the amorphous carbon coating slows down the degradation of Pd catalysts.[3] Moreover, the coating can block big ions such as halide, thus benefiting Pt group metals from resisting halide adsorption, that eventually prevents the dissolution of metal.[4,5]In this work, we examined the gas poisoning effects on coated catalysts. For example, we synthesized carbon-coated Pd-Ni nanoparticles, supported on Vulcan carbon and studied its electrochemical response in 0.1M KOH at room temperature and its tolerance towards CO gas. As a result, Pd-Ni coated had better resistance to passivation compared to the non-coated Pd-Ni catalyst. It also showed that the thickness of the carbon coating layers was sufficient to block the CO absorption in RDE condition initially (Figure 1, black solid line). Only after 150 cycles of accelerated stress test in Ar (AST-Ar, using potential stepping between 0.1 and 1.23 V vs. RHE with a pulse of 3 s at each potential in Ar-saturated electrolyte, 6s/cycles), the passivation that occurred at high potential could cause a small portion of Pd to be “exposed” and adsorb CO (Figure 1, red solid line). After another 150 cycles of AST-Ar (AST 300), more Pd was exposed to CO adsorption but not fully. This proves the carbon-coating layers can protect the nanoparticles from poison contaminant gas such as NOx, SOx, CO, or the COx-like species. Both AFC and PEMFC systems can benefit from this type of catalyst to operate extensively without losing catalytic activity to passivation or pollution issues.

New Materials for Alkaline Fuel Cells from Electroplating Industries Waste Solution Oxygen Reduction Reaction Catalyzed by Pd on Carbon Nanotubes, Graphene and Carbon Black

Issues concerning the energy sector are the focus of international discussions; the progressive depletion of fossil reserves and the increase in energy demand have led to the rise in fuel and electricity prices. In this context, fuel cells are promising candidates for a sustainable future. Oxygen Reduction Reaction (ORR) is the bottle-neck strategic reaction ruling the fuel cell efficiency process. This reaction allows the release of chemical energy in the form of electricity without producing any waste. However, the slow kinetics of ORR require highly effective electrocatalysts for proper boosting. It is well known that best available catalysts, in terms of raw bulk elements, belong to the so-called platinum group metals (PGMs). PGMs are very expensive, hence lowering the PGM content of ORR catalysts is among the most prevalent research focuses [1,2].We propose two different ways to obtain carbon-based ORR catalyst with a low continent of PMGs. The first approach involves the use of Single-Ion catalysts designed by carbon nanotubes functionalized with palladium(II) complexes show [3]. The second approach is totally innovative and aims at recovering precious metals to reduce industrial waste and promote the development of a circular economy. Large quantities of wastewater are produced in electroplating industries. This wastewater not only has to be properly processed before it is released into the environment, but also contains metals like palladium [4]. Using carbon materials and an electroless deposition, palladium can be recovered from the wastewater of the electroplating industry. We focus on carbon black (CB) and two different types of graphene-type materials named as (G4) and (G7). It was found that CB and G4 can recover up to 97% palladium. In this way we obtained hybrid materials containing palladium that could be promising candidates for use as catalysts for the ORR in alkaline fuel cells.New catalysts were treated by preparing a nafion polymeric dispersion and tested with electroanalytical techniques. Rotating ring-disk electrode (RRDE) experiments were performed to investigate the catalytic pathway of ORR and asses the number of exchanged electrons per oxygen molecule. Results confirm that tested materials promote the four-electron reaction pathway and reduce the formation of hydrogen peroxide. These approaches provide the basis for further developments to improve the efficiency of future low-cost catalysts for alkaline fuel cells.[1] Passaponti, M.; Lari, L.; Bonechi, M.; Bruni, F.; Giurlani, W.; Sciortino, G.; Rosi, L.; Fabbri, L.; Vizza, M.; Lazarov, V.K.; et al. Optimisation Study of Co Deposition on Chars from MAP of Waste Tyres as Green Electrodes in ORR for Alkaline Fuel Cells. Energies 2020, 13, 5646, doi:10.3390/en13215646.[2] Bonechi, M.; Giurlani, W.; Vizza, M.; Savastano, M.; Stefani, A.; Bianchi, A.; Fontanesi, C.; Innocenti, M. On the Oxygen Reduction Reaction Mechanism Catalyzed by Pd Complexes on 2D Carbon. A Theoretical Study. Catalysts 2021, 11, 764, doi:10.3390/catal11070764.[3] Savastano, M.; Passaponti, M.; Giurlani, W.; Lari, L.; Calisi, N.; Delgado-Pinar, E.; Serrano, E.S.; Garcia-España, E.; Innocenti, M.; Lazarov, V.K.; et al. Linear, Tripodal, Macrocyclic: Ligand Geometry and ORR Activity of Supported Pd(II) Complexes. Inorganica Chim. Acta 2021, 518, 120250, doi:10.1016/j.ica.2021.120250.[4] De Beni, E.; Giurlani, W.; Fabbri, L.; Emanuele, R.; Santini, S.; Sarti, C.; Martellini, T.; Piciollo, E.; Cincinelli, A.; Innocenti, M. Graphene-Based Nanomaterials in the Electroplating Industry: A Suitable Choice for Heavy Metal Removal from Wastewater. Chemosphere 2022, 292, 133448, doi:10.1016/j.chemosphere.2021.133448.

Poly(arylene alkylene)s Carrying Quaternary Ammoniums via Flexible Phenylpropyl Spacers as Hydroxide Conducting Membranes

Anion exchange membranes (AEM)s are attracting growing research interests as central components in various alkaline energy conversion and storage devices such as AEM fuel cells and water electrolyzers.1,2 Compared to the devices operated under acidic conditions, the alkaline conditions open up for possibilities to use, e.g., nickel and iron catalysts instead of platinum. However, the insufficient hydroxide conductivity and long-term stability of AEMs at elevated temperatures are still hindering a widespread application of these devices.3 An effective strategy to improve AEM properties by structure design is to functionalize hetero-atom free polymer backbones with quaternary ammonium cations via flexible spacers.4-6 In the present work, we have synthesized a series of AEM materials by tethering three different quaternary ammonium cations to poly(arylene alkylene)s via a phenylpropyl spacer (Figure 1a). The Friedel-Crafts acylation and polyhydroxyalkylation employed in the monomer and polymer syntheses are both free of noble metals and have excellent yields. All the polymers prepared in this way formed robust membranes reaching high hydroxide conductivities – up to 175 mS/cm at 80 °C (Figure 1b). PpT-DMP, carrying dimethyl piperidinium cations, was found to have the highest alkaline stability with less than 7% ionic loss after treatment in 7 M aq. NaOH at 90 oC during 240 h. The hydroxide conductivity of PpT-DMP reached 104 mS/cm at an ion exchange capacity (IEC) of 1.79 mequiv./g., which is still quite high. Atom force microscope (AFM) phase imaging revealed a phase separated morphology of PpT-DMP, most probably involving ion-clustering (Figure 1c). In this presentation we will further discuss the synthesis of these polymers, and influence of the phenylpropyl spacer on AEM properties.[1] Xue, J.; Zhang, J.; Liu, X.; Huang, T.; Jiang, H.; Yin, Y.; Qin, Y.; Guiver, M. D. Toward alkaline-stable anion exchange membranes in fuel cells: cycloaliphatic quaternary ammonium-based anion conductors. Electrochem. Energy Rev. 2022, 5, 348-400.[2] Chatenet, M.; Pollet, B. G.; Dekel, D. R.; Dionigi, F.; Deseure, J.; Millet, P.; Braatz, R. D.; Bazant, M. Z.; Eikerling, M.; Staffell, I.; Balcombe, P.; Horn, Y. S.; Schafer, H. Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments. Chem. Soc. Rev. 2022, 51, 4583-4762.[3] Varcoe, J. R.; Atanassov, P.; Dekel, D. R.; Herring, A. M.; Hickner, M. A.; Kohl, P. A.; Kucernak, A. R.; Mustain, W. E.; Nijmeijer, K. N.; Scott, K.; Xu, T.; Zhuang, L. Anion-exchange membranes in electrochemical energy systems. Energy Environ. Sci. 2014, 7, 3135-3197.[4] Dang, H. S.; Jannasch, P. Exploring different cationic alkyl side chain designs for enhanced alkaline stability and hydroxide ion conductivity of anion-exchange membranes. Macromolecules 2015, 48, 5742-5751.[5] Allushi, A.; Pham, T. P.; Olsson, J. S.; Jannasch, P. Ether-free polyfluorenes tethered with quinuclidinium cations as hydroxide exchange membranes. J. Mater. Chem. A 2019, 7, 27164-27174.[6] Lee, W. H.; Kim, Y. S.; Bae, C. Robust Hydroxide Ion Conducting Poly(biphenyl alkylene)s for Alkaline Fuel Cell Membranes. ACS Macro Lett. 2015, 4, 814-818. Figure 1. a) Poly(arylene alkylene)s tethered with different quaternary ammonium cations via phenylpropyl spacers, b) hydroxide conductivity of the AEMs in the fully hydrated state, and c) an AFM phase image of PpT-DMP. Figure 1