Enhancing Polymer Electrolyte Membrane Fuel Cells with Ionic Liquids: A Review.

Polymer electrolyte membrane fuel cells (PEMFCs) represent a promising clean energy solution. However, their widespread adoption faces hurdles related to component optimization. This review explores the pivotal role of ionic liquids (ILs) in enhancing PEMFC performance, focusing on their role in polymer electrolyte membranes, catalyst modification, and other components. By addressing key obstacles, including proton conductivity, catalyst stability, and fuel crossover, ILs provide a pathway towards the widespread commercialization of PEMFCs. In the realm of PEMFC membranes, ILs have shown great potential in improving proton conductivity, mechanical strength, and thermal stability. Additionally, the utilization of ILs as catalyst modifiers has shown promise in enhancing the electrocatalytic activity of electrodes by serving as an effective stabilizer to promote the dispersion of metal nanoparticles, and reduce their agglomeration, thereby augmenting catalytic performance. Furthermore, ILs can be tailored to optimize the catalyst-support interaction, ultimately enhancing the overall fuel cell efficiency. Their unique properties, such as high oxygen solubility and low volatility, offer advantages in terms of reducing mass transport and water management issues. This review not only underscores the promising advancements achieved thus far but also outlines the challenges that must be addressed to unlock the full potential of ILs in PEMFC technology, offering a valuable resource for researchers and engineers working toward the realization of efficient and durable PEMFCs.

Multifunctional Pt3Rh-Co3O4 alloy nanoparticles with Pt-enriched surface and induced synergistic effect for improved performance in ORR, OER, and HER.

Engineering high-performance electrocatalysts to improve the kinetics of parallel electrochemical reactions in low-temperature fuel cells, water splitting, and metal-air battery applications is important and inevitable. In this study, by employing a chemical co-reduction method, we developed multifunctional Pt3Rh-Co3O4 alloy with uniformly distributed ultrafine nanoparticles (2-3 nm), supported on carbon. The presence of Co3O4 and the incorporation of Rh led to a strong electronic and ligand effect in the Pt lattice environment, which caused the d-band center of Pt to shift. This shift improved the electrocatalytic performance of Pt3Rh-Co3O4 alloy. When Pt3Rh-Co3O4/C was used to catalyze the oxygen reduction reaction (E1/2: 0.75 V), oxygen evolution reaction (η10: 290 mV), and hydrogen evolution reaction (η10: 55 mV), it showed greater endurance (mass activity loss of only 7%-17%) than Pt-Co3O4/C and Pt/C catalysts up to 5000 potential cycles in perchloric acid. Overall, the as-prepared Pt3Rh-Co3O4/C showed high multifunctional electrocatalytic potency, as demonstrated by typical electrochemical studies, and its physicochemical properties endorse their extended performance for a wide range of energy storage and conversion applications.

Improving Performance of an Integrated Solar Flow Battery by Cr- and Cu-Doped TiO2 Photoelectrodes.

This work reports on the preparation of Cr-doped TiO2 (Cr−TiO2), Cu-doped (Cu-TiO2), and its utilization in the photoanode of a solar redox flow battery (SRFB). A pure TiO2 electrode, Cr-doped TiO2 electrode, and Cu-doped TiO2 electrode coated with different layers are prepared by the sol-gel method. XRD, XPS, and SEM are used to characterize the relevant data of the electrode. All three electrodes show the structure of the anatase phase, but the Cu-TiO2 and Cr-TiO2 electrodes are more crystalline. Using these materials as photoelectrodes to prepare integrated solar flow cells, the semi-cell and full-cell tests show that the doping of Cr and Cu improves the efficiency and charging current of solar cells. The average charging currents of the Cu-TiO2 and Cr-TiO2 electrodes are 384.20 µA and 450.75 µA, respectively, compared with the TiO2 electrode; this increment reaches values of 71.23% and 100.97%.

Nano-Graphene Layer from Facile, Scalable and Eco-Friendly Liquid Phase Exfoliation Strategy as Effective Barrier Layer for High-Performance and Durable Direct Liquid Alcohol Fuel Cells.

Graphene, in spite of exceptional physio-chemical properties, still faces great limitations in its use and industrial scale-up as highly selective membranes (enhanced ratio of proton conductivity to fuel cross-over) in liquid alcohol fuel cells (LAFCs), due to complexity and high cost of prevailing production methods. To resolve these issues, a facile, low-cost and eco-friendly approach of liquid phase exfoliation (bath sonication) of graphite to obtain graphene and spray depositing the prepared graphene flakes, above anode catalyst layer (near the membrane in the membrane electrode assembly (MEA)) as barrier layer at different weight percentages relative to the base membrane Nafion 115 was utilized in this work. The 5 wt.% nano-graphene layer raises 1 M methanol/oxygen fuel cell power density by 38% to 91 mW·cm-2, compared to standard membrane electrode assembly (MEA) performance of 63 mW·cm-2, owing to less methanol crossover with mild decrease in proton conductivity, showing negligible voltage decays over 20 h of operation at 50 mA·cm-2. Overall, this work opens three prominent favorable prospects: exploring the usage of nano-materials prepared by liquid phase exfoliation approach, their effective usage in ion-transport membrane region of MEA and enhancing fuel cell power performance.

Lutetium-Induced Ultrafine PtRu Nanoclusters with a High Electrochemical Surface Area for Direct Methanol Fuel Cells at Alleviated Temperatures.

PtRu alloys have been recognized as the state-of-the-art catalysts for the methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). However, their applications in DMFCs are still less efficient in terms of both catalytic activity and durability. Rare earth (RE) metals have been recognized as attractive elements to tune the catalytic activity, while it is still a world-class challenge to synthesize well-dispersed Pt-RE alloys. Herein, we developed a novel hydrogen-assisted magnesiothermic reduction strategy to prepare a highly dispersed carbon-supported lutetium-doped PtRu catalyst with ultrafine nanoclusters and atomically dispersed Ru sites. The PtRuLu catalyst shows an outstanding high electrochemical surface area (ECSA) of 239.0 m2 gPt-1 and delivers an optimized MOR mass activity and specific activity of 632.5 mA mgPt-1 and 26 A cmPt-2 at 0.4 V vs saturated calomel electrode (SCE), which are 3.6 and 3.5 times of commercial PtRu-JM and an order higher than PtLu, respectively. These novel catalysts have been demonstrated in a high-temperature direct methanol fuel cell running in a temperature range of 180-240 °C, achieving a maximum power density of 314.3 mW cm-2. The AC-STEM imaging, in situ ATR-IR spectroscopy, and DFT calculations disclose that the high performance is resulted from the highly dispersed PtRuLu nanoclusters and the synergistic effect of the atomically dispersed Ru sites with PtRuLu nanoclusters, which significantly reduces the CO* intermediates coverage due to the promoted water activation to form the OH* to facilitate the CO* removal.

Polyhedron shaped palladium nanostructures embedded on MoO2/PANI-g-C3N4 as high performance and durable electrocatalyst for oxygen reduction reaction.

A hybrid catalyst support anchoring a noble metal catalyst could be a promising material for building interfacial bonding between metallic nanostructures and polymer functionalized carbon supports to improve the kinetics of oxygen reduction reaction (ORR). This study successfully prepared a polyhedron nanostructured Pd and MoO2-embedded polyaniline-functionalized graphitized carbon nitride (PANI-g-C3N4) surface using a chemical reduction method. The Pd-Mo/PANI-g-C3N4 achieved an ORR activity of 0.27 mA µg-1 and 1.14 mA cm-2 at 0.85 V, which were 4.5 times higher than those of commercial 20% Pt/C catalyst (0.06 mA µg-1 and 0.14 mA cm-2). In addition, the Pd-Mo/PANI-g-C3N4 retained âˆ¼ 77.5% of its initial mass activity after 10,000 cycles, with only 30 mV half-wave potential reduction. Further, the engineered potential active sites in the catalyst material verified the significant improvement in the ORR activity of the catalyst with increased life-time, and theoretical calculations revealed that the synergistic effect of the catalytic components enhanced the ORR kinetics of the active sites.

Model development of bioelectrochemical systems: A critical review from the perspective of physiochemical principles and mathematical methods.

Bioelectrochemical systems (BESs) are promising devices for wastewater treatment and bio-energy production. Since various processes are interacted and affect the overall performance of the device, the development of theoretical modeling is an efficient approach to understand the fundamental mechanisms that govern the performance of the BES. This review aims to summarize the physiochemical principle and mathematical method in BES models, which is of great importance for the establishment of an accurate model while has received little attention in previous reviews. In this review, we begin with a classification of existing models including bioelectrochemical models, electronic models, and machine learning models. Subsequently, physiochemical principles and mathematical methods in models are discussed from two aspects: one is the description of methodology how to build a framework for models, and the other is to further review additional methods that can enrich model functions. Finally, the advantages/disadvantages, extended applications, and perspectives of models are discussed. It is expected that this review can provide a viewpoint from methodologies to understand BES models.

Ordered mesoporous Pt-Ru-Ir nanostructures as superior bifunctional electrocatalyst for oxygen reduction/oxygen evolution reactions.

An efficient oxygen bifunctional catalyst Pt-Ru-Ir with ordered mesoporous nanostructures (OMNs) was successfully synthesized by chemical reduction using KIT-6 mesoporous silica as a template. The crystallographic behavior, electronic effects, and microstructure of the catalysts were investigated by XRD, XPS, SEM, and TEM analysis. The influence of OMNs and the effect of Ir content in Pt-Ru-Ir catalyst on both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were investigated. The synergistic and electronic effects play an important role in electrocatalytic performance through the electronic coupling between Pt, Ru and Ir followed by the alloy formation with different lattice strain percentages. Amongst, the OMNs Pt70Ru25Ir5 catalyst exhibits the highest mass activity of 0.21 mA µg-1 and specific activity of 0.33 mA cm-2 for ORR, which are nearly 5-fold greater than those for benchmark Pt/C catalyst. Furthermore, the Pt70Ru25Ir5 demonstrated enhanced OER activity with an overpotential of 470 mV at 10 mA cm-2, an onset potential of 1.70 V, and a Tafel slope of 118 mV dec-1, outperforming commercial IrO2. In addition, the durability of the Pt70Ru25Ir5 catalyst for ORR and OER are found to be extended in comparison with that of other catalysts reported in this work after 6000 cycles. These results demonstrate that the ordered OMNs Pt-Ru-Ir with low Ir content (∼5 wt%) could be a promising oxygen bifunctional catalyst for electrochemical energy conversion and storage applications.

Fabrication of polyoxometalate-modified palladium-nickel/reduced graphene oxide alloy catalysts for enhanced oxygen reduction reaction activity.

Designing advanced nanocatalysts for effectively catalyzing the oxygen reduction reaction (ORR) is of great importance for practical applications of direct methanol fuel cells (DMFCs). In this work, the reduced graphene oxide (rGO)-supported palladium-nickel (Pd-Ni/rGO) alloy modified by the novel polyoxometalate (POM) with Keggin structure (Pd-Ni/rGO-POM) is efficiently fabricated via an impregnation technique. The physical characterizations such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (FESEM-EDX), and transmission electron microscopy (TEM) are utilized to confirm the structure, morphology, and chemical composition of the fabricated samples. The XRD results verify the formation of the POM-modified Pd8Ni2/rGO alloy electro-catalyst with the face-centered-cubic (fcc) structure and average crystallite size of 5.54 nm. The electro-catalytic activities of the nanocatalysts towards ORR in alkaline conditions are evaluated by cyclic voltammetry (CV), rotating disk electrode (RDE), and chronoamperometry (CA) analyses. The synthesized Pd8Ni2/rGO-POM nanomaterial shows remarkably greater ORR catalytic activity and better methanol resistance compared with the Pd8Ni2/rGO and Pd/rGO electro-catalysts. The promoted ORR activity of the Pd8Ni2/rGO-POM sample is attributed to the alloying of Pd and Ni components, the uniform scattering of Pd-Ni nanoparticles on rGO, and the alloyed catalyst being modified with POM. Moreover, these findings demonstrate that the resultant Pd8Ni2/rGO-POM material is attractive as a suitable and cost-effective cathodic catalyst for DMFCs, in which the decorated POMs play a vital role for the enhancement in the catalytic abilities of the nanocatalyst.

Pt-based (Zn, Cu) nanodendrites with enhanced catalytic efficiency and durability toward methanol electro-oxidation via trace Ir-doping engineering.

Pt-based alloy nanomaterials with nanodendrites (NDs) structures are efficient electrocatalysts for methanol oxidation reaction (MOR), however their durability is greatly limited by the issue of transition metals dissolution. In this work, a facile trace Ir-doping strategy was proposed to fabricate Ir-PtZn and Ir-PtCu alloy NDs catalysts in aqueous medium, which significantly improved the electrocatalytic activity and durability for MOR. The as-prepared Ir-PtZn/Cu NDs catalysts showed distinct dendrites structures with the averaged diameter of 4.1 nm, and trace Ir doping subsequently improved the utilization of Pt atoms and promoted the oxidation efficiency of methanol. The electrochemical characterizations further demonstrated that the obtained Ir-PtZn/Cu NDs possessed enhanced mass activities of nearly 1.23 and 1.28-fold higher than those of undoped PtZn and PtCu, and approximately 2.35 and 2.67-fold higher than that of Pt/C in acid medium. More excitingly, after long-term durability test, the proposed Ir-PtZn and Ir-PtCu NDs still retained about 88.9% and 91.6% of its initial mass activities, which further highlights the key role of Ir-doping in determining catalyst performance. This work suggests that trace Ir-doping engineering could be a promising way to develop advanced electrocatalysts toward MOR for direct methanol fuel cell (DMFC) applications.

Numerical study of mass transfer and desorption behaviors in deformable porous media using a coupling lattice Boltzmann model.

The aim of this paper is to investigate the pore-scale mass transfer and desorption behaviors in deformable porous media using a coupling immersed boundary method (IBM)-lattice Boltzmann (LB) scheme. In this numerical model, a three-dimensional multiple-relaxation-time LB model is used to simulate fluid flow in porous media consisting of movable rigid adsorbent particles. To consider the effect of dynamic deformation of a porous structure, an improved immersed boundary method scheme is introduced to describe the fluid-structure interaction at the interface between the carrier gas and moving absorbent particles. Moreover, a LB model for the convection diffusion equation is adopted to consider the mass transfer of adsorbate into the macropores and micropores of the porous adsorbent. This coupled IBM-LB model is used to illustrate the mass transfer and desorption processes in shrinkage deformation of the porous structure caused by the movement of rigid adsorbent particles along different directions. At the initial time, these adsorbent particles have a saturation adsorption amount, and the adsorbate in the macropores has the uniform concentration distribution. The numerical results show that the time history curve of the adsorbate concentration in the macropores can be divided into an upturn period and a downturn period during the dynamic desorption process. In the concentration upturn period governed by Langmuir adsorption kinetics, the shrinkage deformation of the porous structure along different directions has no remarkable effect on the mass transfer and desorption behaviors. However, during the concentration downturn period governed by the mass transfer rate of the adsorbate, the shrinkage deformation of the porous structure obviously decreases the efficiency of the desorption process. In addition, the roles of the deformation direction and morphology of the porous media in the desorption process are illustrated in this work.

Electrochemical Characteristics and Transport Properties of V(II)/V(III) Redox Couple in a Deep Eutectic Solvent: Magnetic Field Effect.

Compared with conventional aqueous electrolytes, deep eutectic solvent (DES) has a wider electrochemical stability window, simple preparation, potential biodegradability, and lower cost, leading to its utilization as electrolyte for non-aqueous redox flow batteries (RFB). However, the large viscosity and inferior transport properties hinder the wide spread of DES electrolyte. To circumvent these issues, various additives as well as external fields can be applied separately or synergistically. This work reports a study on the inclusion of a DC magnetic field to the glycol-based DES electrolyte of a RFB. The effects of magnetic field on the physical and electrochemical characteristics of the electrolyte and the active redox couple on mass transfer are studied by cyclic voltammetry and electrochemical impedance spectroscopy. The experimental results show that the viscosity of the vanadium DES electrolyte decreases and the conductivity increases after adding a magnetic field. With the intensity of the added magnetic field increases, the oxidation and reduction peak current densities of the vanadium DES electrolyte keep increasing. Under the magnetic field intensity of 605 mT, the oxidation peak current density and the reduction peak current density increases 41.56 and 30.74%, respectively, compared with those of no added magnetic field. The ohmic resistance and electrochemical reaction resistance of the vanadium DES electrolyte are reduced when adding the magnetic field, reaching to 40.55 and 43.28%, respectively, with a magnetic field intensity of 605 mT. This study shows an effective yet simple way to improve the physical and electrochemical properties of DES electrolyte, which owns the potential to be widely applied in non-aqueous redox flow batteries.

Scalable Synthesis of Micromesoporous Iron-Nitrogen-Doped Carbon as Highly Active and Stable Oxygen Reduction Electrocatalyst.

Micromesoporous metal-nitrogen-doped carbons have attracted incremental attention owning to their high activities for the electrocatalyzing oxygen reduction reaction (ORR). However, scalable synthesis of micromesoporous metal-nitrogen-doped carbons having superior electrocatalytic activity and stability remains a challenge. Here, an iron-nitrogen-doped carbon with highly electrocatalytic properties was simply prepared by ZnCl2 activation of an in situ polymerized iron-containing polypyrrole (PPy@FeClx) at high temperature. High yields of polypyrrole (∼98 wt %) and iron-nitrogen-doped carbon (∼47 wt %) could be reached. The eutectic state of FeClx-ZnCl2 and its derived ZnFe2O4 maskant played important roles in making micromesopores, scattering iron atoms, and trapping nitrogen atoms, leading to numerous micromesopore defects, a larger specific surface area, a more nitrogen doping content, and active sites for the material. The electrochemical tests and Zn-air battery measurements showed that the micromesoporous iron-nitrogen-doped carbon could achieve much positive onset and half-wave potentials at 0.98 and 0.90 V, respectively, as well as a large current density (6.06 mA/cm2) and good cycling stability. The combination of the iron-nitrogen doping and micromesopore defects by the eutectic salt activation method provided an effective way to scalable synthesize iron-nitrogen-doped carbon as highly active and stable oxygen reduction electrocatalytsts.