Electrochemical Methods Research Articles

Electrochemical Polishing Method for Titanium Alloys with a Microgroove Structure

TI–6AL–4V alloys are widely used in various fields owing to their excellent corrosion resistance, high-temperature resistance, and low-temperature toughness. Herein, a microgroove fixture was used to simulate the microgrooves in a titanium alloy with different aspect ratios to study the influence of the electrolyte flow rate on the polishing effect. The optimization of the electrochemical polishing parameters was conducted using experiments and simulations. The effects of process parameters, such as the concentration of sodium chloride (NaCl) and zinc chloride (ZnCl2), polishing time, and processing voltage, on the quality of the post-polished surface were studied. Experiments were conducted on microgrooves with different aspect ratios under the optimized polishing process parameters. Changes in the surface elements of the microgrooves after polishing were detected. The experimental results indicated that the optimal electrochemical polishing solution flow rate, NaCl concentration, ZnCl2 concentration, polishing time, and processing voltage were 0.2 m/s, 4.0 wt.%, 0.4 wt.%, 8 min, and 90 V, respectively. After 8 min of electrochemical polishing, a TiO2 passivation film was formed on the surface of the microgroove. The surface roughness of the notch and bottom of the microgroove decreased from 250 nm to below 40 nm, with a minimum of 24.5 nm.

Research progress in the detection of trace heavy metal ions in food samples

Food safety is the basis for ensuring human survival and development. The threat of heavy metal ions to food safety has become a social concern with the rapid growth of the economy and the accompanying environmental pollution. Some heavy metal ions are highly toxic even at trace levels and pose significant health risks to humans. Therefore, ultrasensitive detection of heavy metal ions in food samples is important. In this mini-review, recent advances in the analytical methods based on nanomaterials for detecting trace heavy metal ions in food samples are summarized in three categories: electrochemical, colorimetric, and fluorescent methods. We present the features and sensing mechanisms of these three methods, along with typical examples to illustrate their application in the detection of heavy metal ions in foods. This mini-review ends with a discussion of current challenges and future prospects of these approaches for sensing heavy metal ions. The review will help readers understand the principles of these methods, thereby promoting the development of new analytical methods for the detection of heavy metal ions in food samples.

Construction of Metal–Organic Framework as a Novel Platform for Ratiometric Determination of Cyanide

Metal–organic frameworks (MOFs) are frequently utilized as sensing materials. Unfortunately, the low conductivity of MOFs hinder their further application in electrochemical determination. To overcome this limitation, a novel modification strategy for MOFs was proposed, establishing an electrochemical determination method for cyanides in Baijiu. Co and Ni were synergistically used as the metal active centers, with meso−Tetra(4−carboxyphenyl)porphine (TCPP) and Ferrocenecarboxylic acid (Fc−COOH) serving as the main ligands, synthesizing Ni/Co−MOF−TCPP−Fc through a hydrothermal method. The prepared MOF exhibited improved conductivity and stable ratio signals, enabling rapid and sensitive determination of cyanides. The screen−printed carbon electrodes (SPCE) were suitable for in situ and real−time determination of cyanide by electrochemical sensors due to their portability, low cost, and ease of mass production. A logarithmic linear response in the range of 0.196~44 ng/mL was demonstrated by this method, and the limit of detection (LOD) was 0.052 ng/mL. Compared with other methods, the sensor was constructed by a one−step synthesis method, which greatly simplifies the analysis process, and the determination time required was only 4 min. During natural cyanide determinations, recommended readouts match well with GC−MS with less than 5.9% relative error. Moreover, this electrochemical sensor presented a promising method for assessing the safety of cyanides in Baijiu.

Label-free electrochemical biosensor based on green-synthesized reduced graphene oxide/Fe3O4/nafion/polyaniline for ultrasensitive detection of SKBR3 cell line of HER2 breast cancer biomarker

Cancer stands as one of the most impactful illnesses in the modern world, primarily owing to its lethal consequences. The fundamental concern in this context likely stems from delayed diagnoses in patients. Hence, detecting various forms of cancer is imperative. A formidable challenge in cancer research has been the diagnosis and treatment of this disease. Early cancer diagnosis is crucial, as it significantly influences subsequent therapeutic steps. Despite substantial scientific efforts, accurately and swiftly diagnosing cancer remains a formidable challenge. It is well known that the field of cancer diagnosis has effectively included electrochemical approaches. Combining the remarkable selectivity of biosensing components—such as aptamers, antibodies, or nucleic acids—with electrochemical sensor systems has shown positive outcomes. In this study, we adapt a novel electrochemical biosensor for cancer detection. This biosensor, based on a glassy carbon electrode, incorporates a nanocomposite of reduced graphene oxide/Fe3O4/Nafion/polyaniline. We elucidated the modification process using SEM, TEM, FTIR, RAMAN, VSM, and electrochemical methods. To optimize the experimental conditions and monitor the immobilization processes, electrochemical techniques such as CV, EIS, and SWV were employed. The calibration graph has a linear range of 102–106 cells mL−1, with a detection limit of 5 cells mL−1.

Current analytical methods and applications used in the insight of serum proteins interactions with various food additives, pesticides, and contaminants

In recent years, many societies have expressed increasing apprehension regarding the potential negative impacts of food additives, pesticides, and environmental contaminants on human health. Environmental or occupational exposure to these compounds can cause significant adverse effects on human health by causing temporary or permanent changes in the immune system. There is supporting evidence linking pesticides/food ingredients/contaminants-induced immune alterations to the prevalence of diseases associated with changes in immune responses. Hence, it is essential to comprehensively understand the key mechanisms contributing to immune dysregulation induced by these substances, including direct immunotoxicity, endocrine disruption, and antigenicity. The impact of pesticides/food ingredients and contaminants on the human body ranges from mild to severe, depending on their affinity for blood components. These compounds form complexes with blood serum proteins, influencing their metabolism, transport, absorption, and overall toxicity. Numerous studies in the literature have explored the interactions between serum proteins and various molecules, including pesticides, drugs, and food dyes. These investigations employed a range of techniques, including spectroscopy, electrochemical and chromatographic methods as well as molecular modeling and molecular dynamics simulations analyses. This recent review, spanning from 2020 to the present, has been employed to investigate the binding characteristics, mechanisms, and attributes of different food additives, pesticides, and contaminants with serum proteins by using various techniques such as steady-state fluorescence, circular dichroism and ultra-violet spectroscopies, and computational docking methods. The review provides insights into these compounds’ positions and affinities to proteins and possible effects on human health through detailed research studies.

Partial photoelectrocatalytic oxidation of 3‐methylpiridine in green conditions by nanotube/nanowire Ti/TiO2 plates prepared in aqueous, glycerol, or ethylene glycol medium

Nanotube/nanowire structured TiO2 samples on Ti plates were prepared by anodic oxidation in aqueous, glycerol or ethylene glycol medium under different experimental conditions and characterized by XRD, SEM‐EDX, electrochemical methods (photocurrent profiles and electrochemical impedance spectroscopy). The nanostructured TiO2 was built on relatively large Ti plates, and consequently, in some preparation conditions, different morphologic properties were observed in the underside and upside zones of the electrodes, especially in ethylene glycol medium. The electrodes were tested for selective photoelectrocatalytic oxidation of 3‐methylpyridine to 3‐pyridinemethanol, 3‐pyridinemethanal and vitamin B3 in water under UVA irradiation. The best performance was found with the electrode prepared in ethylene glycol/water/NH4F (98/2/0.3 w/w) medium at 36 V potential for 3 h, while the worst was that prepared in aqueous medium which showed the shortest nanostructure length. Unlike photoelectrocatalysis and photocatalysis, no carbonyl products were obtained in electrocatalytic and photolytic experiments. The selectivity values of the products were similar for the various electrodes, while the morphology of the nanotubes/nanowires and their quantity which affects the total active surface area were essential for the substrate conversion. The results also show that the photocurrent intensity, XRD peak intensity, and electrical conductivity are correlated with photoelectrocatalytic activity of the Ti/TiO2 electrodes.

Oxidative MnO2 Template Assisted Electrochemical Fabrication of Graphene/Polypyrrole Supercapacitor Electrodes.

Improving the morphological structure of active materials is a reliable strategy for the fabrication of high-performance supercapacitor electrodes. In this study, we introduce a feasible approach to constructing the graphene/polypyrrole (PPy) composite film implanted onto the current collector through a two-step electrochemical deposition method utilizing MnO2 as an intermediary template. The reduced graphene oxide (rGO) hydrogel film is first hydrothermally grown on a carbon cloth (CC) substrate to obtain a porous rGO@CC electrode on which MnO2 is electrodeposited. Then the as-prepared rGO/MnO2@CC electrode is subjected to the electrochemical polymerization of pyrrole, with MnO2 acting as an oxidizing template to facilitate the oxidative polymerization of pyrrole, ultimately yielding an rGO/PPy composite film on CC. The PPy synthesized via this methodology exhibits a distinctive interconnected structure, resulting in superior electrochemical performance compared with the electrode with PPy directly electrodeposited on rGO@CC. The optimized electrode achieves an impressive specific capacitance of 583.6 F g-1 at 1 A g-1 and retains 83% of its capacitance at 20 A g-1, with a capacitance loss of only 9.5% after 5000 charge-discharge cycles. The corresponding all-solid-state supercapacitor could provide a high energy density of 22.5 Wh kg-1 and a power density of 4.6 kW kg-1, with a capacitance retention of 82.7% after 5000 charge-discharge cycles. Furthermore, the device also demonstrates good flexibility performance upon bending at 90 and 180°. This work presents an innovative method for the preparation of carbon material/conducting polymer electrodes with specific structural characteristics and superior performance.

Toward an Improved Electrocatalytic Determination of Immunomodulator COVID Medication Baricitinib Using Multiwalled Carbon Nanotube Nickel Hybrid.

The study presents a first electrochemical method for the determination of the immunomodulator drug Baricitinib (BARI), crucial in managing COVID-19 patients requiring oxygen support. A unique electrode was developed by modifying graphite carbon nickel nanoparticles (NiNPs) with functionalized multiwalled carbon nanotubes (f.MWCNTs), resulting in nanohybrids tailored for highly sensitive BARI detection. Comparative analysis revealed the superior electrocatalytic performance of the nanohybrid-modified electrode over unmodified counterparts and other modifications, attributed to synergistic interactions between f.MWCNTs and nickel nanoparticles. Under optimized conditions, the sensors exhibited linear detection within a concentration range from 4.00 × 10-8 to 5.56 × 10-5 M, with a remarkably low detection limit of 9.65 × 10-9 M. Notably, the modified electrode displayed minimal interference from common substances and demonstrated high precision in detecting BARI in plasma and medicinal formulations, underscoring its clinical relevance and potential impact on COVID-19 treatment strategies.

Characterization of Electrochemical and Biocompatibility of Zinc Oxide Coating Electrodeposited on Comercial Pure Titanium Alloy

This study examines how the duration of electrodeposition affects the morphology and electrochemical characteristics of zinc oxide coatings applied to a pure titanium substrate. The morphology of the coating and the phases present within it were analyzed using a scanning electron microscope and the X‐ray diffraction technique. The coating’s resistance to corrosion in a phosphate‐buffered saline solution was evaluated using two electrochemical methods: impedance spectroscopy and potentiodynamic polarization tests. The surface roughness of the coated samples was assessed using interferometry. The results demonstrate that an increase in electrodeposition time, ranging from 150 to 1200 seconds, leads to an enhanced texture intensity in the (0002) and (010) planes of the ZnO coating. Furthermore, the thickness of the ZnO crystals and surface roughness increases by factors of 3.25 and 2.79, respectively, as the deposition time is extended. This extended duration results in the formation of larger needle‐shaped and flower‐like ZnO crystals, leading to a significantly non‐uniform structure. Correspondingly, the corrosion rate also increases as the electrodeposition time is extended from 150 to 1200 seconds, rising from 0.001951 to 9.117 µm/year. The lowest corrosion rate (1.654 µm/year) is achieved in coatings deposited for 300 seconds using a potential of 3 V.This article is protected by copyright. All rights reserved.

Using Metalloporphyrin Nanosensors for In Situ Monitoring and Measurement of Nitric Oxide and Peroxynitrite in a Single Human Neural Progenitor Cell.

Nitric oxide (NO) is an inorganic signaling molecule that plays a crucial role in the regulation of numerous physiological functions. An oxidation product of the cytoprotective NO is cytotoxic peroxynitrite (ONOO-). In biological systems, the concentrations of NO and ONOO- are typically transient, ranging from nanomolar to micromolar, and these increases are normally followed by a swift return to their basal levels due to their short life spans. To understand the vital physiological role of NO and ONOO- in vitro and in vivo, sensitive and selective methods are necessary for direct and continuous NO and ONOO- measurements in real time. Because electrochemical methods can be adjusted for selectivity, sensitivity, and biocompatibility in demanding biological environments, they are suitable for real-time monitoring of NO and ONOO- release. Metalloporphyrin nanosensors, described here, have been designed to measure the concentration of NO and ONOO- produced by a single human neural progenitor cell (hNPC) in real time. These nanosensors (200-300 nm in diameter) can be positioned accurately in the proximity of 4-5 ± 1 μm from an hNPC membrane. The response time of the sensors is better than a millisecond, while detection limits for NO and ONOO- are 1 × 10-9 and 3 × 10-9 mol/L, respectively, with a linear concentration response of up to about 1 μM. The application of these metalloporphyrin nanosensors for the efficient measurement of the concentrations of NO and ONOO- in hNPCs is demonstrated, providing an opportunity to observe in real time the molecular changes of the two signaling molecules in situ.

Particle size effect on surface/interfacial tension and Tolman length of nanomaterials: A simple experimental method combining with theoretical.

Surface tension and interfacial tension are crucial to the study of nanomaterials. Herein, we report a solubility method using magnesium oxide nanoparticles of different radii (1.8-105.0nm, MgO NPs) dissolved in pure water as a targeted model; the surface tension and interfacial tension (and their temperature coefficients) were determined by measuring electrical conductivity and combined with the principle of the electrochemical equilibrium method, and the problem of particle size dependence is discussed. Encouragingly, this method can also be used to determine the ionic (atomic or molecular) radius and Tolman length of nanomaterials. This research results disclose that surface/interfacial tension and their temperature coefficients have a significant relationship with particle size. Surface/interfacial tension decreases rapidly with a radius <10nm (while the temperature coefficients are opposite), while for a radius >10nm, the effect is minimal. Especially, it is proven that the value of Tolman length is positive, the effect of particle size on Tolman length is consistent with the surface/interfacial tension, and the Tolman length of the bulk does not change much in the temperature range. This work initiates a new era for reliable determination of surface/interfacial tension, their temperature coefficients, ionic radius, and Tolman length of nanomaterials and provides an important theoretical basis for the development and application of various nanomaterials.

Reviewing neonicotinoid detection with electroanalytical methods.

Neonicotinoids, as the fastest-growing class of insecticides, currently account for over 25% of the global pesticide market. Their effectiveness in controlling a wide range of pests that pose a threat to croplands, home yards/gardens, and golf course greens cannot be denied. However, the extensive use of neonicotinoids has resulted in significant declines in nontarget organisms such as pollinators, insects, and birds. Furthermore, the potential chronic, sublethal effects of these compounds on human health remain largely unknown. To address these pressing issues, it is crucial to explore and understand the capabilities of electrochemical sensors in detecting neonicotinoid residues. Surprisingly, despite the increasing importance of this topic, no comprehensive review article currently exists in the literature. Therefore, our proposed review aims to bridge this gap by providing a thorough analysis of the use of electrochemical methods for neonicotinoid determination. In this review article, we will delve into various aspects of electrochemical analysis, including the influence of electrode materials, employed techniques, and the different types of electrode mechanisms utilized. By synthesizing and analysing the existing research in this field, our review will offer valuable insights and guidance to researchers, scientists, and policymakers alike.

Self-assembled dipeptide grafted nanohybrid material strips for reliable spectroscopic and electrochemical recognition of tryptamine

According to the World Health Organization (WHO), foods high in tryptamine may cause foodborne diseases and abnormal activity in the central nervous system (CNS). The real-time monitoring of tryptamine levels is an emphasized topic among scientific community. In the present work, we report a cost-effective fluorescent paper strips-based methodology impregnated with self-assembled dipeptide-modified (DM1) zinc oxide (ZnO) i.e.DM1@ZnO for the real-time monitoring of tryptamine levels. It is based on an organic-inorganic nanohybrid material of self-assembled N-functionalised dipeptide molecule coated over the surface of ZnO thus tailoring its properties for the detection of tryptamine employing spectroscopic and electrochemical methods. The designed material exhibited a noteworthy response towards tryptamine irrespective of the presence of other biogenic amines (BAs). It selectively displayed blue fluorescence under the 365 nm UV light. On top of that, the detection of tryptamine was also corroborated by its transition to 2-oxytryptamine, as deduced from its electrochemical route. Thus, the proposed paper strip-based methodology unbolts a realistic platform for the efficient recognition of varying levels of tryptamine thus tackling the prima facie reasons for foodborne diseases.

Novel High-Entropy FeCoNiMoZn-Layered Hydroxide as an Efficient Electrocatalyst for the Oxygen Evolution Reaction

The exploration of catalysts for the oxygen evolution reaction (OER) with high activity and acceptable price is essential for water splitting to hydrogen generation. High-entropy materials (HEMs) have aroused increasing interest in the field of electrocatalysis due to their unusual physicochemical properties. In this work, we reported a novel FeCoNiMoZn-OH high entropy hydroxide (HEH)/nickel foam (NF) synthesized by a facile pulsed electrochemical deposition method at room temperature. The FeCoNiMoZn-OH HEH displays a 3D porous nanosheet morphology and polycrystalline structure, which exhibits extraordinary OER activity in alkaline media, including much lower overpotential (248 mV at 10 mA cm−2) and Tafel slope (30 mV dec−1). Furthermore, FeCoNiMoZn-OH HEH demonstrates excellent OER catalytic stability. The enhanced catalytic performance of the FeCoNiMoZn-OH HEH primarily contributed to the porous morphology and the positive synergistic effect between Mo and Zn. This work provides a novel insight into the design of HEMs in catalytic application.

Determination of Trace Cd(II) in Water and Cosmetics based on Au/GO/CuO Nanocomposite Functionalized Electrochemical Sensor

Abstract Cadmium (Cd(II)) is highly toxic to environmental, and while many approaches have been developed to measure cumulative Cd(II) concentration over time, online monitoring of spatiotemporal changes remains challenging. To address this, an electrochemical sensor for determination of ultra-trace Cd(II) was developed, based on gold/graphene oxide/copper oxide (Au/GO/CuO) nanomaterials modifying glassy carbon electrode. CuO nanoparticles were prepared by a green synthesis method using plant extract, and the Au nanoparticles were deposited on the GO/CuO nanosubstrates by an in-situ electrochemical method. The prepared nanocomposites were characterized by field-emission scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The CuO nanoparticles are layered flower-like with an average particle size of 200-500 nm. Au/GO/CuO nanocomposites with high specific surface area and excellent electronic transmission capability enhanced the electrochemical signal of the sensor. Owing to the synergistic effect of Au/GO/CuO, the sensor exhibited good performance to Cd(II) in the ultra-wide range of 5×10-11 - 5×10-7 M with a detection limit of 2×10-11 M. The sensor was successfully quantified for determining Cd(II) with desirable recovery, displaying outstanding long-term stability, high sensitivity, and reproducibility. After validating its accuracy, this sensor was successfully used for detection of Cd (II) in water and cosmetic samples.

A "2-in-1" Bioanalytical System Based on Nanocomposite Conductive Polymers for Early Detection of Surface Water Pollution.

This work proposes an approach to the formation of receptor elements for the rapid diagnosis of the state of surface waters according to two indicators: the biochemical oxygen demand (BOD) index and toxicity. Associations among microorganisms based on the bacteria P. yeei and yeast S. cerevisiae, as well as associations of the yeasts O. polymorpha and B. adeninivorans, were formed to evaluate these indicators, respectively. The use of nanocomposite electrically conductive materials based on carbon nanotubes, biocompatible natural polymers-chitosan and bovine serum albumin cross-linked with ferrocenecarboxaldehyde, neutral red, safranin, and phenosafranin-has made it possible to expand the analytical capabilities of receptor systems. Redox polymers were studied by IR spectroscopy and Raman spectroscopy, the contents of electroactive components were determined by atomic absorption spectroscopy, and electrochemical properties were studied by electrochemical impedance and cyclic voltammetry methods. Based on the proposed kinetic approach to modeling individual stages of bioelectrochemical processes, the chitosan-neutral red/CNT composite was chosen to immobilize the yeast association between O. polymorpha (ks = 370 ± 20 L/g × s) and B. adeninivorans (320 ± 30 L/g × s), and a bovine serum albumin (BSA)-neutral composite was chosen to immobilize the association between the yeast S. cerevisiae (ks = 130 ± 10 L/g × s) and the bacteria P. yeei red/CNT (170 ± 30 L/g × s). After optimizing the composition of the receptor systems, it was shown that the use of nanocomposite materials together with associations among microorganisms makes it possible to determine BOD with high sensitivity (with a lower limit of 0.6 mg/dm3) and detect the presence of a wide range of toxicants of both organic and inorganic origin. Both receptor elements were tested on water samples, showing a high correlation between the results of biosensor analysis of BOD and toxicity and the results of standard analytical methods. The results obtained show broad prospects for creating sensitive and portable bioelectrochemical sensors for the early warning of environmentally hazardous situations based on associations among microorganisms and nanocomposite materials.

Electrochemical decladding of used nuclear fuel

In this study, an electrochemical method for decladding used nuclear fuel (UNF) was investigated by electrochemically oxidizing pieces of zircaloy in a LiF–NaF–ZrF4 (26-37-37 mol%) salt. Electrochemically decladding UNF allows for zirconium (Zr) to be separated from fission products, such that Zr no longer needs to be stored as high-level waste (HLW). As zircaloy samples were oxidized, both the Zr deposited on the cathode and in the bulk salt were checked for the buildup of elements other than Zr to vet this process. The current efficiency of the system was also found to be over 90% and tested samples of zircaloy were oxidized entirely, showing the current used is not wasted on other reactions than oxidizing zircaloy and that the process works to completion.

Electrochemical Oxidative 1,2-Dithiocyanation: Access to Functionalized Alkenes and Alkynes.

Reported herein is the 1,2-dithiocyanation of alkenes and alkynes via an efficient and facile electrochemical method. This approach not only showed a broad substrate scope and good functional-group compatibility but also avoided stoichiometric oxidants. Different from previous reports, various internal alkynes could be tolerated to provide tetra-substituted alkenes. Further gram-scale-up experiments and synthetic transformation demonstrated a potential application in organic synthesis. This process underwent a radical pathway, as evidenced by our mechanistic studies.

Electrochemical Sensors and Biosensors for Identification of Viruses: A Critical Review.

Due to their life cycle, viruses can disrupt the metabolism of their hosts, causing diseases. If we want to disrupt their life cycle, it is necessary to identify their presence. For this purpose, it is possible to use several molecular-biological and bioanalytical methods. The reference selection was performed based on electronic databases (2020-2023). This review focused on electrochemical methods with high sensitivity and selectivity (53% voltammetry/amperometry, 33% impedance, and 12% other methods) which showed their great potential for detecting various viruses. Moreover, the aforementioned electrochemical methods have considerable potential to be applicable for care-point use as they are portable due to their miniaturizability and fast speed analysis (minutes to hours), and are relatively easy to interpret. A total of 2011 articles were found, of which 86 original papers were subsequently evaluated (the majority of which are focused on human pathogens, whereas articles dealing with plant pathogens are in the minority). Thirty-two species of viruses were included in the evaluation. It was found that most of the examined research studies (77%) used nanotechnological modifications. Other ones performed immunological (52%) or genetic analyses (43%) for virus detection. 5% of the reports used peptides to increase the method's sensitivity. When evaluable, 65% of the research studies had LOD values in the order of ng or nM. The vast majority (79%) of the studies represent proof of concept and possibilities with low application potential and a high need of further research experimental work.

Optimisation and effect of ionomer loading on porous Fe–N–C-based proton exchange membrane fuel cells probed by emerging electrochemical methods

The next generation of proton exchange membrane fuel cells (PEMFCs) require a substantial reduction or elimination of Pt-based electrocatalyst from the cathode, where O2 reduction takes place. The most promising alternative to Pt is atomic Fe embedded in N-doped C (Fe–N–C). Successful incorporation of Fe–N–C in PEMFCs relies on a thorough understanding of the catalyst layer properties, both ex situ and in situ, with tailored electrode interface engineering. To help resolve this conundrum, we provide a quantitative protocol on the optimisation of I/C for Fe–N–Cs. It is demonstrated that a high pore volume (3.33 cm3 g−1FeNC) Fe–N–C catalyst requires a sufficiently high ionomer to catalyst mass ratio (I/C, 2.8≤I/C ≤ 4.2) for optimum PEMFC activity under H2/O2. Emerging electrochemical techniques (distribution of relaxation times and Fourier transformed alternating current voltammetry) were used to deconvolute for the first time the trade-off between proton and electron resistance and accessible FeNx active site density with increasing ionomer loading. These findings highlight the significant impact of tuning the I/C ratio based on the catalyst layer properties and feature the power of evolving electrochemical tools for optimising performance in PEMFCs and other electrochemical devices.