Electrochemical science advances最新文献

The influence of the nature of carbon-support materials on the structure and the electrochemical performance of NiMo cathode catalysts is investigated. Carbon materials addressed in this study include Ketjen Black, Vulcan and MWCNT-COOH. A one pot, easily scalable, hydrothermal microwave synthesis with a subsequent hydrogen reduction step was applied for the preparation of the catalyst materials. The structures and compositions of the catalysts were characterized by TEM/SEM, XRD, ICP-OES, BET and STEM-EDX. The performance of the catalysts was tested using rotating disc electrode (RDE) and anion exchange membrane (AEM) single-cell electrolyser to downselect the most active material. The influence of pH, catalyst loading and type of carbon support was investigated to optimize the operating conditions. By increasing the KOH concentration from 0.1 to 1 M in an AEM electrolysis cell, the current density could be more than doubled, whereas the introduction of a carbon support raised the current density by a factor of seven. Finally, it is demonstrated how applying a novel bar-coating preparation of the electrodes in a PGM-free AEM electrolyser enabled a favourable current density of 1 A cm⁻² at 2.04 V. This performance is comparable to earlier systems but requires only a fraction of the catalyst loading.

Equivalent circuit modelling (ECM) of electrochemical impedance spectroscopy (EIS) data is a common technique to describe the state-dependent response of electrochemical systems such as batteries or fuel cells. To use EIS for predictive assessments of the future behaviour of such a system or its state of health (SOH), a more elaborate digital twin model is needed. Developing a robust and continuous SOH estimation poses a formidable challenge. In this study, a framework is presented where ECM parameters are expanded in a high-dimensional Chebyshev space. It facilitates not only a mapping of the state of charge dependence with robust boundary conditions but also an extension towards a more abstract SOH description is possible. Such methods can bridge the gap between the experiment and purely data-driven techniques that do not rely on fitting of experimental data using a priori defined models. In the absence of long-time impedance measurements of a battery, quasi-Monte Carlo sampling can be employed to generate differently aged synthetic battery models with limited experimental impedance data. As additional data becomes available, the space spanning the possible states of a battery can be gradually refined. The developed framework, therefore, allows for the training of big data models starting with very little experimental information and assuming random fluctuations of the model parameters consistent with available data.

Green Hydrogen (H₂) is generally considered to play a key role in enabling sustainable energy storage, as well as a renewable feedstock to various industrial sectors. Accordingly, the production of H₂ by water electrolysis at an industrial scale is a key prerequisite for a transformation of our energy system. With respect to water electrolysis, proton exchange membrane (PEM) electrolysers are generally considered a technology option for the production of green H₂ on a large scale. Prior to market ramp-up PEM electrolysers have to undergo substantial de-risking for a technology ramp-up. For a comprehensive de-risking, a fundamental and holistic understanding of the degradation phenomena of electrolysers on an industrially relevant scale is a prerequisite. Field data with different application-specific load profiles needs to be acquired in order to develop countermeasures against possible degradation patterns induced by the operational mode. This is not only crucial for the more mature PEM technology but also in the future relevant for other more novel membrane electrolysis technologies such as anion exchange membrane (AEM) looking to make the step from laboratory operation to large-scale production and deployment. This editorial aims to outline the current status and general workflow of the de-risking process and serve as an introduction to the topics of this special issue ranging from fundamental studies on degradation processes on the catalyst level up to novel factory concepts for ramping up of electrolyser production.

Conditioning of the membrane electrode assembly (MEA) is an important step to establish functionality and obtain a consistent performance of the proton exchange membrane electrolytic cell (PEMEC) when setting it into operation. On a laboratory scale in an academic context, conditioning encompasses primary pre-treatment of the MEA by chemical or thermal procedures under defined mechanical conditions and, secondarily, the break-in procedure, during which the PEMEC is subjected to initial electrical loads before actual operation. This study demonstrates the effect of MEA conditioning on the short-term performance of PEMEC. The impact of mechanical, chemical and thermal conditions during pre-treatment was investigated for Nafion N115-based MEAs while keeping the break-in procedure invariant for all pre-treatment conditions. The electrochemical characterisation was performed using polarisation curves and electrochemical impedance spectroscopy. The impact of ex situ–before assembly of the cell–versus in situ–after assembly of the cell–conditioning resulted in markedly different mechanical conditions. The experimental results showed an improvement in PEMEC performance by pre-treating the MEA after cell assembly. Compared to pre-treatment with deionised water (DI water) at 60°C, treatment with acidic solution improved the performance, evidenced by a 21 mV reduction in cell voltage at 2 A·cm⁻². When compared with DI water at 60°C, a pre-treatment at 90°C with DI water reduced cell voltage by 23 mV.

The environment in which aircraft are used is very complex, and factors such as high salinity, high humidity atmospheric conditions and mechanical loads applied to the aircraft during flight can lead to damage to the fuselage materials and compromise the safety of the aircraft. A large number of mechanical structural components in aircraft consist of aluminium alloys, which are susceptible to mechanical loads that erode mechanical properties and endanger the integrity of the aircraft. A time-dependent numerical model is developed in this study. The model provides insight into the complex effects of mechanical loading on the kinetics of galvanic coupling corrosion of AA7075 (aluminium alloy). Our results clearly show that mechanical loading accelerates galvanic corrosion, and the galvanic corrosion behaviour of aluminium alloys is significantly accelerated when loading induces plastic deformation; changes in the thickness of the thin liquid film affect the galvanic corrosion of the galvanic coupling model, which is suppressed when the film thickness is increased, and, in general, exhibits a stronger tendency to corrode homogeneously; the galvanic corrosion behaviour of aluminium alloys is significantly accelerated as the area of cathode increases; the simulation also reveals a higher localisation rate of the model when the boundary load is applied compared to the no-load case in the galvanic coupling corrosion behaviour. The numerical methodology illustrated in this study not only serves as a comprehensive tool for interpreting the intricate relationship between mechanical loading and corrosion behaviour, but also provides a framework for a deeper understanding of this multifaceted phenomenon. In practical applications, the model developed in this study can be used to check the safety of aluminium alloy structural components in service, which can be used as a reference for the design of aircraft wing skins.

Oxygen reduction reaction (ORR) is key in many green energy conversion devices like fuel cells and metal-air batteries. Developing cheap and robust electrocatalysts is crucial to expedite the slow ORR kinetics at the cathode. Lately, transition metal (TM) and heteroatom-doped carbon catalysts have surfaced as promising cathode materials for ORR as they display admirable electrocatalytic activity and distinguished properties like tunable morphology, structure, composition and porosity. This review summarizes the recent breakthrough in TM (Fe, Co, Mn and Ni) and heteroatoms (N, S, B, P and F) doping in carbon materials. Moreover, their ORR activity and active sites are inspected for future augmentation in making ORR catalysts for electrochemical devices. The existing challenges and prospects in this field are ratiocinated in conclusion.

Anion exchange membrane water electrolysis (AEMWE) is one of the most promising candidates for green hydrogen production needed for the de-fossilization of the global economy. As AEMWE can operate at high efficiency without expensive Platinum Group Metal (PGM) catalysts or titanium cell components, required in state-of-the-art proton exchange membrane electrolysis (PEMWE), AEMWE has the potential to become a cheaper alternative in large-scale production of green hydrogen. In AEMWE, the porous transport layer and/or micro porous layer (PTL/MPL) has to balance several important tasks. It is responsible for managing transport of electrolyte and/or liquid water to the catalyst layers (CLs), transport of evolving gas bubbles away from the CLs and establishing thermal and electrical connection between the CLs and bipolar plates (BPPs). Furthermore, especially in case the CL is directly deposited onto the MPL, forming a catalyst-coated substrate (CCS), the MPL surface properties significantly impact CL stability. Thus, the MPL is one of the key performance-defining components in AEMWE. In this study, we employed the flexible and easily upscaled technique of atmospheric plasma spraying (APS) to deposit spherical nickel coated graphite directly on a low-cost mesh PTL. Followed by oxidative carbon removal, a nickel-based MPL with superior structural parameters compared to a state-of-art nickel felt MPL was produced. Due to a higher activity of the nickel APS-MPL itself, as well as improved catalyst utilization, a reduction in cell voltage of 63 mV at 2 A cm⁻² was achieved in an AEMWE operating with 1 M KOH electrolyte. This improvement was enabled by the high internal surface area and the unique pore structure of the APS-MPL with a broad pore size distribution as well as the finely structured surface providing a large contacting area to the CLs.

One of the most mature technologies for green hydrogen production is alkaline water electrolysis. However, this process is kinetically limited by the sluggish oxygen evolution reaction (OER). Improving the OER kinetics requires electrocatalysts, which can offer superior catalytic activity and stability in alkaline environments. Stainless steel (SS) has been reported as a cost-effective and promising OER electrode due to its ability to form active Ni-Fe oxyhydroxides during OER. However, it is limited by a high Fe-to-Ni ratio, leading to severe Fe-leaching in alkaline environments. This affects not only the electrode activity and stability but can also be detrimental to the electrolyzer system. Therefore, we investigate the effect of different Ni-coatings on both pure Ni- and SS-supports on the OER activity, while monitoring the extent of Fe-leaching during continuous operation. We show that thin layers of Ni enable enhanced OER activities compared to thicker ones. Especially, a less than 1 µm thick Ni layer on an SS-support shows superior OER activity and stability with respect to the bare supports. X-ray photoelectron spectroscopy reveals traces of oxidized Fe species on the catalyst surface after OER, suggesting that Fe from the SS may be incorporated into the layer during operation, forming active Ni-Fe oxyhydroxides with a very low Fe leaching rate. Utilizing inductively coupled plasma-optical emission spectroscopy, we prove that thin Ni layers on SS decrease Fe leaching whereas the Fe from the uncoated SS-support dissolves into the electrolyte during operation. Thus, OER active and stable electrodes can be obtained while maintaining a low Fe concentration in the electrolyte. This is particularly relevant for application in high-performance electrolyzer systems.

Most commonly, electrochemical CO₂ reduction is performed in a three-compartment setup employing gas diffusion electrodes (GDEs) to decrease mass transport limitations of the gaseous reactant CO₂ to the reaction interface. However recently, there has been a rising number of investigations on suitable membrane electrode assemblies (MEAs) to overcome ohmic potential losses caused by the electrolyte gaps in the systems. While the significant majority of MEAs exhibited in literature is based on catalyst-coated gas diffusion layers, this work presents an approach that does not require a likewise support. On the basis of a catalyst suspension similar to mixtures already employed for GDE production on industrial level, a method to directly transfer the resulting catalyst layers to the membrane is developed. The Faradaic efficiency of carbon monoxide, i.e. target product formation of GDEs manufactured according to a similar procedure, can be matched or even exceeded for individual modifications of the exchange MEAs. Simultaneously, the cell potentials can be remarkably decreased in this setup. By gradual adaptation of the fabrication procedure, the influence of important manufacturing parameters is unraveled, also discussing the effect of hydrogen permeation through the membrane.