The Fe3+ role in decreasing the activity of Nafion-bonded IrO2 catalyst for proton exchange membrane water electrolyser

Fe³⁺ is a common ion contaminant for the proton exchange membrane water electrolyser (PEMWE). In this work, three-electrode-system was employed to study the effect of Fe³⁺ on Nafion-bonded IrO₂ catalyst which is conventional anode catalyst for PEMWE. Study results showed that Fe³⁺ contamination decreased IrO₂ catalytic activity significantly only when the following two conditions were both satisfied: 1) Nafion resin exists in working electrode; 2) working electrode potential was over 1.471 V (vs. NHE) which is around the initial voltage of oxygen evolution reaction (OER). Besides, the contaminated working electrode activity was recovered to about 16% by being immersed into 3 M H₂SO₄ solution, but it was recovered to about 59% by ethanol washing method. These study results revealed that Fe³⁺ plays a role of catalyst for H₂O₂ production during OER process, which leads to Nafion resin decomposition. The degradation products covered working electrode surface, and thus decreased effective active sites of IrO₂. Nafion degradation was further confirmed by analyzing 1) F⁻ content in anode water and 2) FTIR of contaminated Nafion membrane.     

The effects of ionomer content on PEM water electrolyser membrane electrode assembly performance

In this study, the effects of Nafion^® ionomer content in membrane electrode assemblies (MEAs) of polymer electrolyte membrane (PEM) water electrolyser were discussed. The MEAs were prepared with a catalyst coated membrane (CCM) method. The catalysts inks with Nafion ionomer could form uniform coatings deposited on the membrane surfaces. SEM and area EDX mapping demonstrated that anode catalyst coating was uniformly distributed, with a microporous structure. The contents of Nafion ionomer were optimized to 25% for the anode and 20% for cathode. A current density of 1 A cm⁻² was achieved at terminal voltage 1.586 V at 80 °C in a PEMWE single cell, with Nafion 117, Pt/C as cathode, and Ru_0.7Ir_0.3O₂ as anode.     

Production of hydrogen and carbon nanofibers through the decomposition of methane over activated carbon supported Pd catalysts

Hydrogen has been produced by decomposing methane thermocatalytically at 1123 K in the presence of activated carbon supported Pd catalysts (Samples coded as Pd5 and Pd10 respectively) procured from SRL Chemicals, India. The studies indicated that the Pd10 catalyst has higher catalytic activity and life for methane decomposition reaction at 1123 K and volume hourly space velocity (VHSV) of 1.62 L/hr?g. An average methane conversion of 50 mol % has been obtained for Pd10 catalyst at the above reaction conditions. SEM and TEM-EDXA images of Pd10 catalyst after methane decomposition showed formation of carbon nanofibers. XRD of the above catalyst revealed, moderately crystalline peaks of Pd which may be responsible for the increase in the catalytic life and the formation of carbon nanofibers.     

Poly(ethylene glycol) modified activated carbon for high performance proton exchange membrane fuel cells

A high water retention membrane is developed by co-assembling poly(ethylene glycol) (PEG) grafted activated carbon (AC-PEG) with Nafion. The AC-PEG is prepared via a sol–gel process. The use of PEG as a transporting medium in AC-PEG shows a largely improved water retention ability, a higher proton conductivity and a reduced swelling ratio, making it well suited for proton exchange membrane fuel cells (PEMFCs). Further, the composite membranes show improved mechanical properties at high temperature, thus ensuring the structural stability of membranes during the fuel cell operation. Compositional optimized AC-PEG/Nafion composite membrane (15 wt% compared to Nafion) demonstrates a better performance than the commercially available counterpart, Nafion 212, in fuel cell measurements. To identify the key factor of the improved performance, current interrupt technique is used to quantitatively verify the changes of resistance under different relative humidity environment.     

WC as a non-platinum hydrogen evolution electrocatalyst for high temperature PEM water electrolysers

Tungsten carbide (WC) nanopowder was tested as a non-platinum cathode electrocatalyst for polymer electrolyte membrane (PEM) water electrolysers, operating at elevated temperatures. It was prepared in thermal plasma reactor with confined plasma jet from WO₃ precursor in combination with CH₄ carburizing agent. The results of the investigation showed that the activity of tungsten carbide as cathode electrocatalyst increases significantly with temperature and this effect is more pronounced than for platinum, especially, at 150 °C.     

Hydrogen production by advanced proton exchange membrane (PEM) water electrolysers—Reduced energy consumption by improved electrocatalysis

Proton exchange membrane (PEM) water electrolysis systems offers several advantages over traditional technologies including greater energy efficiency, higher production rates, and more compact design. Normally in these systems, the anode has the largest overpotential at typical operating current densities. By development of the electrocatalytic material used for the oxygen evolving electrode, great improvements in efficiency can be made. We find that using cyclic voltammetry and steady state polarisation analysis, enables us to separate the effects of true specific electrocatalytic activity and active surface area. Understanding these two factors is critical in developing better electrocatalytic materials in order to further improve the performance of PEM water electrolysis cells. The high current performance of a PEM water electrolysis cell using these oxides as the anode electrocatalyst has also been examined by steady state polarisation measurements and electrochemical impedance spectroscopy. Overall the best cell voltage obtained is 1.567 V at 1 A cm⁻² and 80 °C was achieved when using Nafion 115 as the electrolyte membrane.     

Gold as an efficient hydrogen isotope separation catalyst in proton exchange membrane water electrolysis

The development of proton exchange membrane water electrolysis (PEMWE) offers an updating potential for electrolytic hydrogen isotope separation. However, it has a significantly lower separation factor than the traditional alkaline water electrolysis. In this study, we propose gold as a promising cathodic catalyst for efficient hydrogen isotope separation in PEMWE. Au/C has a protium-to-deuterium (H/D) separation factor of 7.47 in PEMWE, about twice that of Pt/C. In addition, the full cell's electrochemical performance is comparable to that of its Pt/C counterpart. The separation mechanism in PEMWE is explained by the transitional hydrogen evolution reaction mechanism from Heyrovsky to Tafel for Pt and the unchangeable Volmer mechanism for Au. The high separation factor for Au is also calculated by the H/D zero-point vibrational energy difference between transition state and reaction state through a simple density functional theory calculation. This work offers an effective strategy to improve hydrogen isotope separation efficiency in PEMWE.     

Optimization and aging of Pt nanowires supported on single-walled carbon nanotubes as a cathode catalyst in polymer electrolyte membrane water electrolyser

A catalyst material containing platinum nanowires supported on single-walled carbon nanotubes (CNTs) is tested thoroughly for the use as a cathode catalyst for polymer electrolyte membrane water electrolyser (PEMEL). The Nafion ionomer content, the platinum to CNT ratio and the thickness of the catalyst layer (CL) is optimized. Long-term measurement with constant current and start-stop cycling of the optimized CL is performed in order to study the durability of the catalyst material. The CLs are characterized ex-situ with TEM, XRD and Raman spectroscopy. During the constant current operation, platinum experiences Ostwald ripening type of degradation and during the cycling, particle agglomeration. The magnitude of platinum degradation is, however, lower than for a commercial Pt/C type of catalyst. Moreover, the CNTs are subjected to carbon corrosion, but the rate of corrosion is observed to be decreasing. Therefore, carbon nanotubes are considered more suitable support material for the cathode catalyst of PEMELs.     

Enhancement of efficiency and power output of hydrogen fuelled proton exchange membrane (PEM) fuel cell using oxygen enriched air

This paper deals with the effects of the oxygen-enriched air (up to 50% oxygen by mass) along with other operating parameters (hydrogen flow rate, temperature, and relative humidity) on the performance of hydrogen-fuelled proton exchange membrane (PEM) fuel cell. The active area of a fuel cell considered was 50 cm² with three cells in series connections. The air was supplied with O₂ enriched from 23% to 50% at the cathode. The voltage obtained with the respective enriched air was 2.52 and 2.80 V respectively. The optimum oxygen enrichment was found as 45%. The stack temperature plays a significant role on performance improvement and the optimum temperature was found as 50 °C. The voltage efficiency and power output were improved by 9% and 33% with 45% oxygen-enriched air. Electrochemical impedance spectroscopy was used to analyze the impedance behavior of the fuel cell with the variable current demand. The bode plot indicates current dominates voltage at low oxygen-enriched air (25%) and vice-versa at high-enriched air. The inductive effect was dominating at the low frequency and overtaken by the capacitive effects at the higher frequency. These results would be useful to develop a dedicated fuel cell with the oxygen-enriched air.     

Systematic assessment of the anode flow field hydrodynamics in a new circular PEM water electrolyser

In this work, we investigated the key underlying flow characteristics of a circular unit cell proton exchange membrane (PEM) water electrolyser. In particular, we focused on investigating anode flow field design using computational fluid dynamics (CFD) tool. Transient, 3D single phase fluid flow simulation results were presented, and in-house experiments were conducted for validation against CFD simulation data identifying key performance parameters of the PEM water electrolyser: uniform water distribution, pressure drop and hydraulic retention time. The effects of the water flow rate, inlet and outlet sizing and different number of inlet and outlet configurations were considered. The main observation from the study was discussed to provide insight into the factors affecting the flow pattern. Among the studied flow field design cases, it was found that the average pressure drop decreased with increase in number of inlets, also flow profile can be grouped into different set, depending on number of inlets. The correlation between pressure drop and mean velocity profile for different inlet and outlet configurations provides a useful basis to properly design the high performance PEM water electrolyser.     

Response behaviour of proton exchange membrane water electrolysis to hydrogen production under dynamic conditions

Hydrogen production via proton exchange membrane water electrolysis (PEMWE) coupled with renewable energy sources is gaining considerable attention due to its high current densities and flexible responses. This study investigated the voltage responses of PEMWE under dynamic conditions. Three comprehensive performance parameters were adopted to determine the response behaviours of PEMWE devices, including the total response time (TRT), the voltage stability (V_max - V_min), and the difference between the voltages seen for dynamic and static conditions (ΔV = V_dynamic - V_static). The obtained results showed that with small step currents (ΔI = 1 A) and low currents (I < 9 A), PEMWE presented better responses. The TRT was less than 30 s, (V_max - V_min) was less than 10 mV, and ΔV was less than 20 mV. Increasing the amplitude of the step current increased the response time and reduced the voltage stability during electrolysis. The Joule heat produced by the inner resistance have been responsible for the different response behaviours of the PEMWE devices. A durability test showed that after a square wave operated for 300 h, significant degradation of the PEMWE response was observed by comparing the voltage response parameters. Electrochemical characterization studies indicated increases in the static voltage, resistance, and Tafel slope, which were consistent with the degradation of the PEMWE response.     

System modelling and performance assessment of green hydrogen production by integrating proton exchange membrane electrolyser with wind turbine

This investigation delves into the production of green hydrogen with the aid of a polymer electrolyte membrane electrolyzer with its source of energy harnessed from wind using a vertical axis wind turbine (VAWT). The integrated numerical approach was adopted in the simulation environment of MATLAB, Simulink, and Simscape™ to develop the comprehensive mathematical model of the system. The component-level models are linked to the electrolyser, and wind turbines are modelled distinctively considering their efficiencies. The study first explores current types of electrolysers, from their operational characteristics to their merits and demerits. The Proton Exchange Membrane Electrolysers were recommended as the best electrolysis alternative due to their fast start-up time, and the technology being matured. Various power electronics required in connecting the energy from the wind turbine to the electrolyser was equally discussed. Some of these notable power electronics include the Permanent Magnet Synchronous Generators (PMSG), Full Bridge Diode Rectifier, as well as DC–DC Buck Boost Converter. The study was conducted at Warwickshire area as the location for the installation of the Proton Exchange Membrane Electrolyser System. It was however deduced that the performance of the electrolyser was predominant at higher temperatures but lower pressures. The intensity of wind also had a direct correlation to the overall performance of the electrolyser. In summary, for the wind turbine under investigation, at 1 bar pressure and operating temperature of 20 °C, 65,770 L of hydrogen was produced and this is equivalent to 4656.3 kg of hydrogen or 156.4 kWh of energy.     

Investigation of supported IrO2 as electrocatalyst for the oxygen evolution reaction in proton exchange membrane water electrolyser

Indium tin oxide (ITO) was used as a support for IrO₂ catalyst in the oxygen evolution reaction. IrO₂ nanoparticles were deposited in various loading on commercially available ITO nanoparticle, 17–28 nm in size using the Adam's fusion method. The prepared catalysts were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The BET surface area of the support (35 m²/g) was 3 times lower than the unsupported IrO₂ (112.7 m²/g). The surface area and electronic conductivity of the catalysts were predominantly contributed by the IrO₂. The supported catalysts were tested in a membrane electrode assembly (MEA) for electrolyser operation. The 90% IrO₂-ITO gave similar performance (1.74 V@1 A/cm²) to that of the unsupported IrO₂ (1.73 V@1 A/cm²) in the MEA polarisation test at 80 °C with Nafion 115 membrane which was attributed to a better dispersion of the active IrO₂ on the electrochemically inactive ITO support, giving rise to smaller catalyst particle and thereby higher surface area. Large IrO₂ particles on the support significantly reduced the electrode performance. A comparison of TiO₂ and ITO as support material showed that, 60% IrO₂ loading was able to cover the support surface and giving sufficient conductivity to the catalyst.     

Effect of hydrogen additive on methane decomposition to hydrogen and carbon over activated carbon catalyst

The effect of H₂ addition on CH₄ decomposition over activated carbon (AC) catalyst was investigated. The results show that the addition of H₂ to CH₄ changes both methane conversion over AC and the properties of carbon deposits produced from methane decomposition. The initial methane conversion declines from 6.6% to 3.3% with the increasing H₂ flowrate from 0 to 25 mL/min, while the methane conversion in steady stage increases first and then decreases with the flowrate of H₂, and when the H₂ flowrate is 10 mL/min, i.e. quarter flowrate of methane, the methane conversion over AC in steady stage is four times more than that without hydrogen addition. It seems that the activity and stability of catalyst are improved by the introduction of H₂ to CH₄ and the catalyst deactivation is restrained. Filamentous carbon is obtained when H₂ is introduced into CH₄ reaction gas compared with the agglomerate carbon without H₂ addition. The formation of filamentous carbon on the surface of AC and slower decrease rate of surface area and pores volume may cause the stable activity of AC during methane decomposition.     

Additive manufacturing of bipolar plates for hydrogen production in proton exchange membrane water electrolysis cells

Water electrolysis is a process that can produce hydrogen in a clean way when renewable energy sources are used. This allows managing large renewable surpluses and transferring this energy to other sectors, such as industry or transport. Among the electrolytic technologies to produce hydrogen, proton exchange membrane (PEM) electrolysis is a promising alternative. One of the main components of PEM electrolysis cells are the bipolar plates, which are machined with a series of flow distribution channels, largely responsible for their performance and durability. In this work, AISI 316L stainless steel bipolar plates have been built by additive manufacturing (AM), using laser powder bed fusion (PBF-L) technology. These bipolar plates were subjected to ex-situ corrosion tests and assembled in an electrolysis cell to evaluate the polarization curve. Furthermore, the obtained results were compared with bipolar plates manufactured by conventional machining processes (MEC). The obtained experimental results are very similar for both manufacturing methods. This demonstrates the viability of the PBF-L technology to produce metal bipolar plates for PEM electrolyzers and opens the possibilities to design new and more complex flow distribution channels and to test these designs in initial phases before scaling them to larger surfaces.     

Technical feasibility of a proton battery with an activated carbon electrode

The technical feasibility of a small-scale ‘proton battery’ with a carbon-based electrode is demonstrated for the first time. The proton battery is one among many potential contributors towards meeting the gargantuan demand for electrical energy storage that will arise with the global shift to zero greenhouse emission, but inherently variable, renewable energy sources. Essentially a proton battery is a reversible PEM fuel cell with an integrated solid-state electrode for storing hydrogen in atomic form, rather than as molecular gaseous hydrogen in an external cylinder. It is thus a hybrid between a hydrogen-fuel-cell and battery-based system, combining advantages of both system types. In principle a proton battery can have a roundtrip energy efficiency comparable to a lithium ion battery. The experimental results reported here show that a small proton battery (active area 5.5 cm²) with a porous activated carbon electrode made from phenolic resin and 10 wt% PTFE binder was able to store in electrolysis (charge) mode very nearly 1 wt% hydrogen, and release on discharge 0.8 wt% in fuel cell (electricity supply) mode. A significant design innovation is the use of a small volume of liquid acid within the porous electrode to conduct protons (as hydronium) to and from the nafion membrane of the reversible cell. Hydrogen gas evolution during charging of the activated carbon electrode was found to be very low until a voltage of around 1.8 V was reached. Future work is being directed towards increasing current densities during charging and discharging, multiple cycle testing, and gaining an improved understanding of the reactions between hydronium and carbon surfaces.     

Modification of single wall carbon nanotubes (SWNT) for hydrogen storage

Due to unique structural, mechanical and electrical properties of single wall carbon nanotubes, SWNTs, they have been proposed as promising hydrogen storage materials especially in automotive industries. This research deals with investing of CNT’s and some activated carbons hydrogen storage capacity. The CNT’s were prepared through natural gas decomposition at a temperature of 900?C over cobalt-molybdenum nanoparticles supported by nanoporous magnesium oxide (Co–Mo/MgO) during a chemical vapor deposition (CVD) process. The effects of purity of CNT (80–95%wt.) on hydrogen storage were investigated here. The results showed an improvement in the hydrogen adsorption capacity with increasing the purity of CNT’s. Maximum adsorption capacity was 0.8%wt. in case of CNT’s with 95% purity and it may be raised up with some purification to 1%wt. which was far less than the target specified by DOE (6.5%wt.). Also some activated carbons were manufactured and the results compared to CNTs. There were no considerable H₂-storage for carbon nanotubes and activated carbons at room-temperature due to insufficient binding between H₂ molecules carbon nanostructures. Therefore, hydrogen must be adsorbed via interaction of atomic hydrogen with the storage environment in order to achieve DOE target, because the H atoms have a very stronger interaction with carbon nanostructures.     

Study on electrochemical and mass transfer coupling characteristics of proton exchange membrane (PEM) fuel cell based on a fin-like electrode surface

Proton exchange membrane (PEM) Fuel cells are widely used because of its environmental protection and high efficiency. In the present study, a novel fin-like structure of the electrode surface is investigated by establishing the theoretical model and numerical simulating. For this purpose, the influence of different fin spacing and pressure boost on the performance of the PEM fuel cell is analyzed by numerical simulation. Results show that increasing pressure of cathode or both side experiences greater performance improvement compared to the other cases, and the maximum values of power density during both conditions is founding for fin density 1/1, followed by fin density 1/12, then last the basic model. Furthermore, the analysis shows that increasing CL surface area combined with cathode pressurization is the best strategy for fuel cell performance optimization. The fin structure under the condition of cathode pressurization can effectively reduce the transmission resistance and over potential of the fuel cell by theoretical calculation, which is coinciding well with the simulation results.     

Numerical studies on an air-breathing proton exchange membrane (PEM) fuel cell stack

Air-breathing proton exchange membrane (PEM) fuel cells provide for fully or partially passive operation and have gained much interest in the past decade, as part of the efforts to reduce the system complexity. This paper presents a detailed physics-based numerical analysis of the transport and electrochemical phenomena involved in the operation of a stack consisting of an array of vertically oriented air-breathing fuel cells. A comprehensive two-dimensional, nonisothermal, multi-component numerical model with pressurized hydrogen supply at the anode and natural convection air supply at the cathode is developed and validated with experimental data. Systematic parametric studies are performed to investigate the effects of cell dimensions, inter-cell spacing and the gap between the array and the substrate on the performance of the stack. Temperature and species distributions and flow patterns are presented to elucidate the coupled multiphysics phenomena. The analysis is used to determine optimum stack designs based on constraints on desired performance and overall stack size.