The oil bath thermal cycling absorption process design and separation process research

Thermal cycling absorption process (TCAP) has been developed for years to support the separation of hydrogen isotopes, which has the characteristics of high separation efficiency and high recovery rate. The design of separation column structure, heating and cooling (H&C) system and technological parameters are the basis of TCAP technical process study and are the key points of TCAP engineering research. In this work, an improved separation system has been designed and built based on an oil bath H&C system for the first time. The separation column in this facility is 45 m long and the packing weight in the column is up to 8 kg. The separation experiments were carried out based on this facility, and the process parameters were adjusted according to the size of the separation column, which proved the superior performance of this facility. The separation experiments show that for 50% D₂ - 50% H₂ feed gas, the deuterium abundance can reach to 99% and the steady state extraction can be realized in production mode with the processing capacity over 400 standard L per day. Another experiment has been carried out with 1% D₂ - 99% H₂ feed gas, and the deuterium abundance exceeded 10%, verifying the separation ability at low abundance deuterium feed gas. Furthermore, the extraction rate can reach to 25% column capacity when the deuterium abundance in production gas is 5%.     

Hydrogen isotopic effect during the graphite high-temperature corrosion in water vapours

This paper presents the results on a study the processes of physicochemical interactions of water with graphite. The main regularities of the formation of H₂, HD and D₂ molecules on the graphite surface were determined. It was shown that the fraction of D₂ and HD in the gaseous outcome increases in the process of heating, and the quasi-equilibrium state of the graphite's absorption of hydrogen isotopes at the initial stages of interaction is significant: the flow of dissolved atoms into the sample volume is higher than the desorption flow. We suppose that this is due to the higher rate of dissolution of hydrogen atoms in the volume of graphite. We also estimated also the separation factor for the graphite surface-volume system for hydrogen atoms, which was 1.53 for the selected experimental conditions. The temperature dependence of the effective rate constant K_s for the formation of hydrogen isotope molecules in the interaction of graphite with water vapour in the range of 1100 °C–1200 °C was determined. It turned out that K_S(D₂) > K_S(HD) > K_S(H₂).     

Enhanced hydrogen storage by a variable temperature process

We present a simple method of variable temperature process that can potentially enhance the hydrogen storage properties of a large variety of solid state materials. In this approach, hydrogen gas is first introduced at about room temperature, which is followed by a gradual increase to a preset maximum temperature value, T_max. Using this approach, we investigated hydrogen absorption properties of vertically aligned arrays of magnesium nanotrees and nanoblades fabricated by glancing angle deposition (GLAD) technique, and conventional Mg thin film. Weight percentage (wt%) storage values were measured by quartz crystal microbalance (QCM). After exposing Mg samples to H₂ at 30 bar and 30 °C, dynamic absorption measurements were conducted as the temperature was increased from 30 °C to maximum values of T_max = 100, 200, and 300 ^°C all within 150 min. QCM measurements revealed that variable temperature method results in significant improvements in hydrogen storage values over the ones obtained by conventional constant temperature process. At a low effective temperature T_eff = 165 °C (T_max = 300 °C), we achieved storage values of 6.19, 4.76, and 2.79 wt% for Mg nanotrees, nanoblades, and thin film, respectively.     

Tailoring thermal resistance of porous materials with void filling for improved hydrogen adsorption

Porous materials such as 5A molecular sieve (5A) display huge thermal resistance due to high porosity and lots of voids between grains that is negative to hydrogen isotope separation engineering. Generally, introducing thermal conductive fillers contributes to reducing thermal resistance while results in decreasing volume ratio of porous materials and then certainly causes declined hydrogen adsorption capacity. Here, a liquid polydimethylsiloxane (PDMS) is pressed into the voids between 5A grains, which is further developed into a silicon, oxygen and carbon (SiOC) structure suffering from 350 °C sintering. 5A/SiOC composite at 10 wt% polydimethylsiloxane (5A/SiOC10) displays 0.74 W/mK of thermal conductivity, which is about 300% higher than that of neat 5A. More importantly, enhanced rather than reduced hydrogen adsorption capacities at a fixed volume of the composite are determined. 5A/SiOC10 shows adsorption capacities of H₂ (175.4 mL/cm³) and D₂ (188.4 mL/cm³) while neat 5A shows that of H₂ (171.6 mL/cm³) and D₂ (165.8 mmol/cm³) at 77 K with 1 bar. Besides, enhanced thermal conductivity of porous materials shortens the cycle time of hydrogen isotope separation that contributes to reducing energy consumption. This work proposes a novel strategy on void filling to tailor thermal resistance of porous materials, which open a window to improve hydrogen isotope separation with thermal management materials.     

Highly selective adsorption of D2 from hydrogen isotopes mixture in a robust metal bistriazolate framework with open metal sites

Deuterium has numerous applications in industry and scientific research. However, the conventional methods for separation hydrogen isotopes face the problems of low selectivity and high energy consumption. Recently, microporous material adsorption separation technology provides an efficient way for the separation of hydrogen isotopes. Herein, we prepared the metal bistriazolate framework Ni₂Cl₂BBTA, featuring a high density of coordinatively unsaturated Ni²⁺ sites. Interactions between the open metal sites and hydrogen render this material excellent separation ability for the capture of D₂ from the hydrogen isotopes mixture, with the D₂ over H₂ selectivity up to 4.5 at 77 K and 4.0 at 87 K respectively. Notably, recycle experiments show that this material has great potential in the application of hydrogen isotope separation, owing to its good structural stability and reusability.     

Membrane separation processes for the benefit of the sulfur–iodine and hybrid sulfur thermochemical cycles

Thermochemical cycles have been proposed as processes for the manufacture of hydrogen from water in which the only other effluent is oxygen. In this paper, membrane-based technologies are described that have the promise of enabling the further development of thermochemical cycle processes. Membranes have been studied for the concentration of hydriodic acid (HI) and sulfuric acid using pervaporation. In this work, Nafion^® and sulfonated poly(ether ether ketone) (SPEEK) membranes have effectively concentrated HI at temperatures as high as 134 °C (407 K) without any significant degradation of transport behavior. Additionally, sulfuric acid has been concentrated using Nafion^® membranes at 100 °C (373 K). Measured fluxes of water and separation factors are commercially competitive and have been characterized with respect to acid concentration in the feed streams. Further, hydrogen permeability is discussed at 300 °C (573 K) with the goal of providing a method for the removal of the product gas from HI in the decomposition step, thus increasing the productivity of the equilibrium-limited reaction.     

One-pot synthesis of pure phase molybdenum carbide (Mo2C and MoC) nanoparticles for hydrogen evolution reaction

Herein, we report the one-step synthesis of pure phase molybdenum carbide (Mo₂C and MoC) nanoparticles via the in-situ carburization reduction route without using any reducing agent. The X-ray diffraction (XRD) results confirm the formation of pure phase Mo₂C and MoC at 800 °C for 8 h and 15 h respectively. The as-synthesized powders have been investigated for hydrogen production and energy storage applications. The pure phase Mo₂C shows high performance towards the hydrogen evolution reaction (HER) with a Tafel slope of 129.7 mV dec⁻¹ however, MoC exhibits a low activity towards HER with a Tafel slope of 266 mV dec⁻¹. Both the phases show high stability up to 5000 cyclic voltammetry (CV) cycles in the potential range of 0–0.4 V. In the case of MoC, the specific capacitance increases during the initial 2000 CV cycles which may be attributed to the electrode activation during the CV test. The Mo₂C powder shows a double layer capacitance (C_dl) value of 2.47 mF cm⁻² and a specific capacitance of 2.24 mF g⁻¹. The MoC phase shows a higher C_dl value of 8.99 mF cm⁻² and a specific capacitance of 8.17 mF g⁻¹.     

Cold-rolled magnesium hydride strips decorated with cold-sprayed Ni powders for solid-state-hydrogen storage

The present work reports for the first time application of cold spray coating for doping plastically deformed Mg-strips by different concentrations of fine Ni powders. For present study, Mg rods were cold-rolled for 300 passes and then coated by Ni fine powders, using a cold spray process operated at 150 °C under high argon gas pressure. The Ni powders were pelted into Mg-substrate through the high-velocity jet at a speed of 500 m/s. Under these preparation conditions, Ni powders were plastically deformed at the surface of Mg strips to create numerous pores and cavities, worked as hydrogen diffusion gateway. The as-coated Mg sheets with 3-Ni layers (5.28 wt%) possessed good hydrogenation/dehydrogenation kinetics, implied by a short absorption/desorption time (5.1/11 min) of 6.1 wt% hydrogen at 150 °C/10 bar and 200 °C/200 mbar, respectively. The fabricated solid-state hydrogen storage nanocomposite strips revealed good cyclability of achieving 600 cycles at 200 °C without failure of degradation.     

Investigation of hydrothermal carbonization and chemical activation process conditions on hydrogen storage in loblolly pine-derived superactivated hydrochars

While the challenge of storing hydrogen in inexpensive and renewable adsorbents is relentlessly pursued by researchers all over the world, application of hydrochar derived from biomass is also gaining attention as it can be subsequently chemically activated using activating agents like KOH in order to tailor the development of favorable porosity. However, the synergistic effect of hydrothermal carbonization (HTC) process conditions as well as KOH activating conditions on the development of surface morphology is required to be assessed with the application of such porous superactivated hydrochars in hydrogen storage application. In this study, highly porous superactivated hydrochars were fabricated from inexpensive and abundant loblolly pine. Loblolly pine was hydrothermally carbonized at 180 °C, 220 °C and 260 °C and the hydrochars were then activated at different experimental conditions of 700 °C, 800 °C and 900 °C using solid KOH to loblolly pine hydrochar ratio of 2:1, 3:1 and 4:1 to produce superactivated hydrochars. Superactivated hydrochars as well as loblolly pine and its corresponding hydrochars underwent physicochemical analysis as well as surface morphology analysis by SEM and nitrogen adsorption isotherms at 77 K in order to investigate the effect on BET, pore volume, and pore size distribution due to various process conditions. The superactivated hydrochars were then analyzed to quantify total hydrogen storage capacity of these materials at 77 K and up to pressure of 55 bar. Porosity of superactivated hydrochars were as high as 3666 m²/g of BET specific surface area (SSA), total pore volume of 1.56 cm³/g and micropore volume of 1.32 cm³/g with the hydrogen storage capacity of 10.2 wt% at 77 K and 55 bar. It was conclusive from principal component analysis that higher HTC temperature with moderate activation condition demonstrated favorability in developing porous superactivated hydrochars for hydrogen storage applications.     

A novel cathode catalyst for aluminum-air fuel cells: Activity and durability of polytetraphenylporphyrin iron (II) absorbed on carbon black

A polytetraphenylporphyrin iron (II) (PTPPFe) oxygen reduction reaction (ORR) catalyst for aluminum-air fuel cells (AAFCs) is prepared. Thermogravimetric analysis results show that PTPPFe is stable at temperatures below 600 °C. X-ray photoelectron spectroscopy reveals that the active site of PTPPFe/C is Fe–N₄ in the porphyrin ring. Rotating disk electrode measurements in 1 mol L⁻¹ NaOH solution demonstrate that the initial potential for ORR is 0.142 V vs. Hg/HgO/OH⁻ (1 mol L⁻¹ KOH, 0.098 V vs. NHE) at 20 °C, and that ORR mainly occurs through a four-electron process. The half-wave potentials for PTPPFe/C and the Pt/C catalyst are 0.071 and 0.079 V, respectively. Almost no performance degradation is observed over continuous cyclic voltammetry at 10 000 cycles, linear sweep voltammetry at 200 cycles, and 60 h of chronoamperometry test. After durability tests, the ultraviolet–visible spectrum of PTPPFe does not change from the initial characteristics. The discharge performance of AAFC has a power density of 47.5 mW cm⁻² at 20 °C in 6 mol L⁻¹ NaOH electrolyte solution. During continuous discharge for 10 h, the potential of AAFC decreases by less than 0.01 V at 40 mA cm⁻².     

Cobalt oxide as photocatalyst for water splitting: Temperature-dependent phase structures

This study investigated the best phases of cobalt oxide for the photochemical and photoelectrochemical (PEC) water-splitting reaction. Cobalt oxide was produced via a hydrothermal process of cobalt nitrate hexahydrate and then annealed at different temperatures from 450 °C to 950 °C. The Co₃O₄ phase was produced during pre-annealing and annealing at 450 °C. The mixed phase of Co₃O₄ and CoO was produced during annealing at 550 °C and 650 °C, and pure CoO was produced during annealing from 750 °C to 950 °C. The Co₃O₄ phase produced the highest photocurrent density with a value of 1.15 mA cm⁻² at a −0.4 V potential bias vs. Ag/AgCl. This value two times higher than that reported by other researchers at the same potential bias. Furthermore, the highest rate of hydrogen collected by Co₃O₄ was ~272.6 μmol h⁻¹ g⁻¹ after 8 h photocatalytic process. The amount of collected hydrogen was stable until 12 h of the process.     

Thermal conductivity measurements of magnesium hydride powder beds under operating conditions for heat storage applications

One of the major issues of the change in energy politics is the storage of renewable energy in order to facilitate a continuous energy supply to the grid. An efficient way to store energy (heat) is provided by the usage of Thermochemical Energy Storage (TES) in metal hydrides. Energy is stored in dehydrogenated metal hydrides and can be released by hydrogenation for consumption. One prominent candidate for high temperature (400 °C) heat storage is magnesium hydride. It is a well-known and investigated material which shows high cycling stability over hundreds of cycles. It is an abundant material, non-toxic and easy to prepare in bigger scales. One of the major drawbacks for heat storage applications is the low heat transfer capability of packed beds of magnesium hydrides. In this work we present results of effective thermal conductivity (ETC) which were measured under hydrogen pressure up to 25 bar and temperatures up to 410 °C in order to meet the operating conditions of magnesium hydride as a thermochemical heat storage material. We could show that the effective thermal conductivity of a magnesium hydride – hydrogen system at 410 °C and 25 bar hydrogen increases by 10% from 1.0 W m⁻¹ K⁻¹ to 1.1 W m⁻¹ K⁻¹ after 18 discharging and charging cycles. In dehydrogenated magnesium hydride this increase of the thermal conductivity was found to be at 50% from 1.20 W m⁻¹ K⁻¹ to 1.80 W m⁻¹ K⁻¹ at 21 bar hydrogen. These data are very important for the design and construction of heat storage tanks based on high temperature metal hydrides in the future.     

Novel nanocomposite materials for oxygen and hydrogen separation membranes

Design of oxygen and hydrogen separation membranes is the point of current interest in producing syngas from biofuels. Nanocomposites with a high mixed ionic-electronic conductivity are known to be promising materials for these applications. This work aims at studying performance of oxygen and hydrogen separation membranes based on nanocomposites PrNi_0.5Co_0.5O_3-δ + Ce_0.9Y_0.1O_2-δ and Nd_5.5WO_11.25-δ + NiCu alloy, respectively. A high and stable performance promising for the practical application was demonstrated for these membranes. For oxygen separation membrane CH₄ conversion is up to 50% with H₂ content in the outlet feed being up to 25% at 900 °C. For reactor with hydrogen separation membrane complete EtOH conversion was achieved at T ∼ 700 °C even at the highest flow rate, and a high hydrogen permeation (≥1 ml H₂ cm⁻² min⁻¹) was revealed.     

Ternary transition metal alloy FeCoNi nanoparticles on graphene as new catalyst for hydrogen sorption in MgH2

The present investigation deals with the synthesis of ternary transition metal alloy nanoparticles of FeCoNi and graphene templated FeCoNi (FeCoNi@GS) by one-pot reflux method and there use as a catalyst for hydrogen sorption in MgH₂. It has been found that the MgH₂ catalyzed by FeCoNi@GS (MgH₂: FeCoNi@GS) has the onset desorption temperature of ~255 °C which is 25 °C and 100 °C lower than MgH₂ catalyzed by FeCoNi (MgH₂: FeCoNi) (onset desorption temperature 280 °C) and the ball-milled (B.M) MgH₂ (onset desorption temperature 355 °C) respectively. Also MgH₂: FeCoNi@GS shows enhanced kinetics by absorbing 6.01 wt% within just 1.65 min at 290 °C under 15 atm of hydrogen pressure. This is much-improved sorption as compared to MgH₂: FeCoNi and B.M MgH₂ for which hydrogen absorption is 4.41 wt% and 1.45 wt% respectively, under the similar condition of temperature, pressure and time. More importantly, the formation enthalpy of MgH₂: FeCoNi@GS is 58.86 kJ/mol which is 19.26 kJ/mol lower than B.M: MgH₂ (78.12 kJ/mol). Excellent cyclic stability has also been found for MgH₂: FeCoNi@GS even up to 24 cycles where it shows only negligible change from 6.26 wt% to 6.24 wt%. A feasible catalytic mechanism of FeCoNi@GS on MgH₂ has been put forward based on X-ray diffraction (XRD), Raman spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Photoelectron Spectroscopy (XPS), and microstructural (electron microscopic) studies.     

Temperature dependence of sensing properties of hydrogen-sensitive extended-base heterojunction bipolar transistors

A planar-type metal-semiconductor-metal (MSM) hydrogen sensor forming on the collector layer was employed as an extended base (EB) of the InGaP-GaAs heterojunction bipolar transistors (HBTs). Then, hydrogen sensing transistors integrated were proposed and studied. After introducing sensing properties of the EB-hydrogen sensor, various sensing current gains defined were addressed for our hydrogen sensing transistor. Instead of the base current, N₂ and/or hydrogen-containing gases were used as a parameter while measuring common-emitter characteristics of the hydrogen sensing transistor at various temperatures. Experimental results show that maximum sensing base current gains in 1% H₂/N₂ is 330 at 25 °C while it is enhanced to 1800 at 50 °C, then to 2300 at 80 °C, and finally to 2800 at 110 °C. In contrast, a peak sensing collector current gain is as high as 1.2 × 10⁵ (4.3 × 10⁴) in 1% (0.01%) at 110 °C. In addition, response times obtained from the sensing diode (base) and collector currents in 0.01% H₂/N₂ are 485 (490) and 745 s at 25 °C. Together with important features including one power supply and low-power consumption, the proposed hydrogen sensing transistor is very promising for applications in detecting hydrogen.     

Facile process to utilize carbonaceous waste as a carbon source for the synthesis of low cost electrocatalyst for hydrogen production

Low cost non-noble metal electrocatalysts are highly desirable for the sustainable production of hydrogen as a renewable energy source. Molybdenum carbide (Mo₂C) has been considered as the promising non-noble metal electrocatalyst for the hydrogen production via hydrogen evolution reaction (HER) through water splitting. The nanostructured nitrogen (N) incorporated carbon (C) coupled with Mo₂C is the potential candidate to boost the HER activity and electrode material for the energy conversion applications. In this work, nitrogen incorporated carbon coated Mo₂C (Mo₂C@C/N) has been synthesized in an eco-friendly way using waste plastic as the carbon source. The pure phase Mo₂C@C/N has been synthesized at 700 and 800 °C for 10 h. The relatively higher temperature synthesized phase shows enhanced HER activity with lower Tafel slope (72.9 mVdec⁻¹) and overpotential of 186.6 mV to drive current density of 10 mAcm⁻². It also exhibits stability up to 2000 cyclic voltammetry (CV) cycles and retains the current density with negligible loss for 10 h. The higher temperature synthesized phase exhibits higher electrochemical active surface area (ECSA) and enhanced HER kinetics.     

Voltage degradation of high-temperature PEM fuel cells operating at 200 °C under constant load and start-stop conditions

High temperature proton exchange membrane fuel cells (HT-PEM) offer significant advantages over conventional low temperature fuel cells (LT-PEM), including improved fuel impurity tolerance and increased electrode kinetics. These advantages enable use of reformate fuels with potentially lower costs and simplified handling versus ultra-pure hydrogen fuel required for LT-PEM. Although HT-PEM fuel cell operation has been demonstrated at temperatures above 120 °C, relatively few studies have focused on operation at 200 °C or higher where fuel impurity tolerance is maximized, but at the cost of accelerated performance degradation. To help address this research gap, the present study investigated the voltage degradation of HT-PEM fuel cells operating at 200 °C and 0.4 A/cm² under continuous load conditions, and at 200 °C and 0.6 A/cm² during start-stop cycling. Results based on triplicate measurements show an average constant load degradation rate of 102 μV/h, as compared to literature values of 10 μV/h or less at lower temperature and current density. The start-stop experiments showed relatively high degradation rates per cycle up to 50 cycles, with decreasing average degradation rates over 80 and 100 cycles.     

Superior catalysis of NbN nanoparticles with intrinsic multiple valence on reversible hydrogen storage properties of magnesium hydride

Magnesium hydride, as a potential solid state hydrogen carrier has attracted great attention around the world especially in the energy storage domain due to the high hydrogen storage capacity and the good cycling stability. But kinetic and thermodynamic barriers also impede the practical application and development of MgH₂. Nanoscale catalysts are deemed to be the most effective measure to overcome the kinetic barrier and lower the temperature required for hydrogen release in MgH₂. NbN nanoparticles (~20 nm) with intrinsic Nb³⁺-N and Nb⁵⁺-N were prepared using the molten salt method and used as catalysts in the MgH₂ system. It is found that the NbN nanoparticles exhibit a superior catalytic effect on de/rehydrogenation kinetics for the MgH₂/Mg system. About 6.0 wt% hydrogen can be liberated for the MgH₂+5NbN sample within 5 min at 300 °C, and it takes 12 min to desorb the same amount of hydrogen at 275 °C. Meanwhile, the MgH₂+5NbN sample can absorb 6.0 wt% hydrogen within 16 min at 150 °C, and absorb 5.0 wt% hydrogen within 24 min even at 100 °C. Particularly, the catalyzed samples exhibit excellent hydrogen absorption/desorption kinetic stability. After multiple cycles, there is no kinetic attenuation and the hydrogen capacity remains at about 6.0 wt%. It is demonstrated that the NbN nanoparticles with intrinsic multiple valence can be the critical effect in improving the hydrogen storage kinetics of MgH₂. The stability of Nb₄N₃ phase and Nb³⁺-N and Nb⁵⁺-N valence states can ensure a stable catalytic effect in the system.     

Cerium hydride generated during ball milling and enhanced by graphene for tailoring hydrogen sorption properties of sodium alanate

In this study, NaAlH₄?based hydrogen storage materials with dopants were prepared by a two-steps in-situ ball milling method. The dopants adopted included Ce, few layer graphene (FLG), Ce + FLG, and CeH_2.51. The hydrogen storage materials were studied by non-isothermal and isothermal hydrogen desorption measurements, X-ray diffractions analysis, cycling sorption tests, and morphology analysis. The hydrogen storage performance of the as-prepared NaAlH₄ with Ce addition is much better than that with CeH_2.51 addition. This is due to that the impact of Ce occurs from the body to the surface of the materials. The addition of FLG further enhances the impact of Ce on the hydrogen storage performance of the materials. The hydrogen storage capacity, hydrogen sorption kinetics, and cycle performance of NaAlH₄ with Ce + FLG additions are all better than NaAlH₄ materials with the addition of either Ce or FLG alone. The NaAlH₄ with Ce and FLG addition starts to release hydrogen at 85 °C and achieves a capacity of 5.06 wt% after heated to 200 °C. The capacity maintains at 4.91 wt% (94.7% of the theoretical value) for up to 8 cycles. At 110 °C, the material can release isothermally a hydrogen capacity of 2.8 wt% within 2 h. The activation energies for the two hydrogen desorption steps of NaAlH₄ with Ce and FLG addition are estimated to be 106.99 and 125.91 kJ mol^?1 H₂, respectively. The related mechanisms were studied with first-principle and experimental methods.     

Branched poly(ether ether ketone) based anion exchange membrane for H2/O2 fuel cell

High-performance anion exchange membranes (AEMs) are in need for practical application of AEM fuel cells. Novel branched poly(ether ether ketone) (BPEEK) based AEMs were prepared by the copolymerization of phloroglucinol, methylhydroquinone and 4,4′-difluorobenzophenone and following functionalization. The effects of the branched polymer structures and functional groups on the membrane's properties were investigated. The swelling ratios of all the membranes were kept below 15% at room temperature and had good dimensional stability at elevated temperatures. The branching degree has almost no effect on the dimensional change, but plays a great role in tuning the nanophase separation structure. The cyclic ammonium functionalized membrane showed a lower conductivity but a much better stability than imidazolium one. The BPEEK-3-Pip-53 membrane with the branching degree of 3% and piperidine functionalization degree of 53% showed the best performances. The ionic conductivity was 43 mS cm⁻¹ at 60 °C. The ionic conductivity in 1 M KOH at 60 °C after 336 h was 75% of its initial value (25% loss of conductivity), and the IEC was 83% of its initial value (17% loss of IEC), suggesting good alkaline stability. The peak energy density (60 °C) of the single H₂/O₂ fuel cell with BPEEK-3-Pip-53 membrane reached 133 mW cm⁻² at 260 mA cm⁻².