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Recently, many studies have been published regarding electrochemical oxygen reduction reaction for generating hydrogen peroxide (H2O2) using gas diffusion electrodes (GDEs) for various applications. Sodium salts solved in deionized water were usually used as supporting electrolytes. In technical applications, however, tap water‐based electrolytes with hardeners are particularly relevant and have only been considered in a few studies to date. In this work, we investigated the influence of hardeners on H2O2‐generation at 150 mA cm−2 and were able to show that scaling occurs predominantly on the GDE‐surface and not in its pore structure. With the novel method in electrochemical synthesis by using complexing agents to bind hardeners, we were able to significantly reduce the scaling. Even after 10 h of operation, the reactor still achieves a faradaic efficiency (FE) of above 70 % (>67 mg h−1 cm−2), comparable to the experiments without hardeners and complexing agents in the electrolyte. Furthermore, we demonstrate that the complexing agents are not electrochemically converted at the carbon‐based GDE and behave inertly. If the cell is operated with complexing agents and rinsed with acidic liquid (anolyte) between batches, scaling can be completely avoided. [ABSTRACT FROM AUTHOR]

The electrochemical regeneration of reduced nicotinamide adenine dinucleotide (NADH) using [Rh(Cp*)(bpy)Cl]+ holds significant promise for the industrial synthesis of chiral chemicals. However, challenges persist due to the high consumption of NADH and the limited efficiency of its cyclic regeneration, which currently hinder widespread application. To address these obstacles, based on in‐situ growth of 3D ordered metal‐organic framework (NU‐1000) on the surface of graphite felt, [Rh(Cp*)(bpy)Cl]+ were immobilized on the Zr6 nodes of NU‐1000 by solvent‐assisted ligand incorporation (SALI), and applied in a flow bioreactor. Moreover, we employ a gas diffusion electrode (GDE) to oxidize H2, providing a clean proton source for the electrochemical regeneration of NADH. Consequently, highly efficient enzymatic electrocatalytic synthesis of L‐lactate was achieved when coupled with L‐lactate dehydrogenases (LDH) as a model reaction, and the total turnover number (TTN) reached 19600 and 1750 for [Rh(Cp*)(bpy)Cl]+ and NAD+ after 48 h, corresponding to a high turnover frequency (TOF) of 2350 h−1 and 210 h−1 for [Rh(Cp*)(bpy)Cl]+ and NAD+, respectively. This work provides new insights for the construction of efficient enzymatic electrosynthesis systems in industrial production. [ABSTRACT FROM AUTHOR]

As ammonia continues to gain more and more interest as a promising hydrogen carrier compound, so does the electrochemical ammonia oxidation reaction (AmOR). To avoid the liberation of H2 in a reverse Haber–Bosch reaction under release of the energetically more favorable N2, we propose the oxidation of ammonia to value‐added nitrite (NO2−), which is usually obtained during the Ostwald process. We investigated the anodic oxidation of gaseous ammonia directly supplied to a gas diffusion electrode (GDE) using a variety of compositionally different multi‐metal catalysts coated on Ni foam under the simultaneous formation of H2 at the cathode. This will double the amount of H2 per ammonia molecule while applying a lower overpotential than that required for water electrolysis (1.4–1.8 V vs. RHE at 50 mA ⋅ cm−2). A selectivity study demonstrated that some of the catalyst compositions were able to produce significant amounts of NO2−, and further investigations using the most promising catalyst composition Nif_AlCoCrCuFe integrated within a GDE demonstrated up to 88 % Faradaic efficiency for NO2− at the anode coupled to close to 100 % Faradaic efficiency for the cathodic H2 production. [ABSTRACT FROM AUTHOR]

CO2 electroreduction (CO2RR) to high‐value chemicals by renewable energy is a promising route for achieving carbon cycling. Traditional two‐dimensional planar electrodes applied in CO2RR are faced with problems of high mass transfer resistance, carbonate precipitation, flooding, and complicated structures, seriously limiting their CO2RR efficiency and application. Three‐dimensional hollow fiber gas diffusion electrodes (HFGDEs) are promising candidates due to their rich specific surface area, low mass transfer resistance, simplified component, and no flooding trouble, which are beneficial for achieving high current density as well as high CO2RR efficiency. In this review, we provide inspirations and positive paradigms for the rational design of HFGDE toward CO2RR by following part: 1. The mechanism of CO2RR. 2. The classification of the typical metal‐based CO2RR catalysts. 3. The preparation process of HFGDEs. 4. Recent advanced HFGDE studies for CO2RR. 5. Challenges at this stage and future development of HFGDEs towards accelerating application of industrial CO2 reduction electrolyzers. [ABSTRACT FROM AUTHOR]

Water electrolysis plays a central role in the transition to a fossil‐free society, but there are significant challenges to overcome in order to increase its availability on a large scale. Alkaline water electrolysis is a mature and scalable technology, although it has several disadvantages compared to electrolyzers working in acidic environments. In particular, the use of highly alkaline aqueous electrolytes can lead to corrosion, and the achieved current densities are relatively low. This study addresses the latter limitation by introducing a gas diffusion electrode (GDE) setup as a novel development tool that bridges the gap between research and practical applications in commercial devices such as fuel cells and electrolyzers. A high surface area Ni foam catalyst that can sustain exceptional oxygen evolution reaction (OER) current densities of up to 4 A cm−2 in a quasi‐steady‐state within our GDE setup operating in an alkaline environment is presented. The high performance of this Ni‐based benchmark catalyst is attributed to its deposition onto a mesh‐like porous transport layer (PTL) via hydrogen‐templated electrodeposition. This forms a porous foam‐like structure that augments the mass transport of the gaseous reactants at the GDE. [ABSTRACT FROM AUTHOR]

Abstract This research is a significant step forward in understanding how the electrochemical cell setup influences CO2 conversion. The performance of Cu–Zn–Al metal oxide-based catalysts was compared in two reactor configurations: a gas diffusion electrode (GDE) cell with an aqueous electrolyte and a Membrane Electrode Assembly (MEA) cell operating in the gas phase without catholyte. The different operations induced significant morphological and crystalline structural changes, profoundly impacting the catalytic behaviour. The MEA configuration, for instance, led to the formation of a higher Cu0/Cu1+ ratio in the catalysts, promoting C–C coupling for C2H4 production. Conversely, the GDE operation favoured alcohol (ethanol and methanol) production by balancing copper oxidation states formed in situ in the presence of the aqueous catholyte. Zn and Al oxides also played a role in stabilising the resulting Cu species, some of which remained oxidised on the electrode surface. These findings underscore the crucial influence of varying cell operation conditions on catalyst reconstruction, shaping the quantity of Cu0 + Cu1+ species formed in situ to tailor catalyst selectivity.

The use of gas diffusion electrodes (GDEs) in microbial fuel cells (MFCs) can improve their cell performance, but tends to cause fouling. In order to allow long-term stable operation, the search for antifouling methods is necessary. Therefore, an antibacterial coating with ammonium compounds is investigated. Within the first 30 days of operation, the maximum measured power density of a GDE with antibacterial ionomer was 606 mW m−2. The GDE without an antifouling treatment could only reach a maximum of 284 mW m−2. Furthermore, there was an optimum in the loading amount with ionomer below 2.6 mg cm−2. Further investigations showed that additional aeration of the GDEs by a fan had a negative effect on their performance. Despite the higher performance, the antibacterial coating could not prevent biofilm growth at the surface of the GDE. The thickness of the biofilm was only reduced by 14–16%. However, the weight of the biofilm on the treated GDEs was 62–80% less than on a GDE without an antifouling treatment. Consequently, the coating cannot completely prevent fouling, but possibly leads to a lower density of the biofilm or prevents clogging of the pores inside the electrodes and improves their long-term stability. [ABSTRACT FROM AUTHOR]

Being an efficient approach to the utilization of hydrogen energy, the hydrogen oxidation reaction (HOR) is of particular significance in the current carbon‐neutrality time. Yet the mechanistic picture of the HOR is still blurred, mostly because the elemental steps of this reaction are rapid and highly entangled, especially when deviating from the thermodynamic equilibrium state. Here we report a strategy for decoding the HOR mechanism under operando conditions. In addition to the wide‐potential‐range I–V curves obtained using gas diffusion electrodes, we have applied the AC impedance spectroscopy to provide independent and complementary kinetic information. Combining multidimensional data sources has enabled us to fit, in mathematical rigor, the core kinetic parameter set in a 5‐D data space. The reaction rate of the three elemental steps (Tafel, Heyrovsky, and Volmer reactions), as a function of the overpotential, can thus be distilled individually. Such an undocumented kinetic picture unravels, in detail, how the HOR is controlled by the elemental steps on polarization. For instance, at low polarization region, the Heyrovsky reaction is relatively slow and can be ignored; but at high polarization region, the Heyrovsky reaction will surpass the Tafel reaction. Additionally, the Volmer reaction has been the fastest within overpotentials of interest. Our findings not only offer a better understanding of the HOR mechanism, but also lay the foundation for the development of improved hydrogen energy utilization systems. [ABSTRACT FROM AUTHOR]

This research is a significant step forward in understanding how the electrochemical cell setup influences CO2 conversion. The performance of Cu–Zn–Al metal oxide-based catalysts was compared in two reactor configurations: a gas diffusion electrode (GDE) cell with an aqueous electrolyte and a Membrane Electrode Assembly (MEA) cell operating in the gas phase without catholyte. The different operations induced significant morphological and crystalline structural changes, profoundly impacting the catalytic behaviour. The MEA configuration, for instance, led to the formation of a higher Cu0/Cu1+ ratio in the catalysts, promoting C–C coupling for C2H4 production. Conversely, the GDE operation favoured alcohol (ethanol and methanol) production by balancing copper oxidation states formed in situ in the presence of the aqueous catholyte. Zn and Al oxides also played a role in stabilising the resulting Cu species, some of which remained oxidised on the electrode surface. These findings underscore the crucial influence of varying cell operation conditions on catalyst reconstruction, shaping the quantity of Cu0 + Cu1+ species formed in situ to tailor catalyst selectivity. [ABSTRACT FROM AUTHOR]

Transition metal‐coordinated nitrogen sites on carbon catalysts (M‐N‐C) hold potential for CO2 electroreduction (CO2ER), but optimal morphology and active sites are unclear. We introduce a novel approach, developing zeolitic imidazolate framework‐8 (ZIF‐8)‐derived carbon catalysts with Fe‐N and graphitic‐N sites (Fe2‐NC) via molecular confinement and thermal activation. Fine‐tuning ZIF‐8 size and activation temperature yielded 44.98% active N sites. The 300 nm Fe2‐NC catalyst displayed outstanding CO2‐to‐CO conversion, with a 170 mV overpotential and 94.3% Faradaic efficiency at −0.5 V, outperforming state‐of‐the‐art materials. Enhanced CO2ER kinetics and conductivity contributed to this superiority. Results highlight the correlation between maximum CO Faradaic efficiency and cumulative Fe‐N/graphitic‐N sites, dependent on size and activation. The 300 nm Fe2‐NC in a gas diffusion electrode‐loaded flow cell achieved a 15.3‐fold CO partial current density increase. In a Zn‐CO2 battery, the 300 nm Fe2‐NC demonstrated a peak power density of 0.618 mW cm−2, showcasing energy storage potential. [ABSTRACT FROM AUTHOR]

CO2 electrolysis to value‐added chemicals and fuels shows tremendous potential to store renewable electricity. It features with H2O as the hydrogen source of CO2 electroreduction. Here, we aim at the effect of the hydrophobicity‐tuned catalyst microenvironment in gas diffusion electrode (GDE) on boosting CO2 electrolysis. The hydrophobic polytetrafluoroethylene (PTFE) nanoparticles are introduced in the Sn catalyst layer of GDE. The PTFE‐modified GDE compared to the non‐PTFE electrode delivers a higher HCOOH Faraday efficiency and lower overpotential at current densities of 50–250 mA cm−2. A two‐dimensional axisymmetric model jointly with electrochemical impedance spectroscopy is developed to provide mechanistic insights into the hydrophobicity regulation. The simulated polarization current densities are in keeping with experimental results. The boosted CO2 electrolysis is attributed to the decrease of the distance from the gas–liquid phase boundary to the electrocatalyst. The understanding of the catalyst microenvironment established here can be generalized to other gas‐involved electrocatalytic reactions. [ABSTRACT FROM AUTHOR]

Water electrolysis plays a central role in the transition to a fossil‐free society, but there are significant challenges to overcome in order to increase its availability on a large scale. Alkaline water electrolysis is a mature and scalable technology, although it has several disadvantages compared to electrolyzers working in acidic environments. In particular, the use of highly alkaline aqueous electrolytes can lead to corrosion, and the achieved current densities are relatively low. This study addresses the latter limitation by introducing a gas diffusion electrode (GDE) setup as a novel development tool that bridges the gap between research and practical applications in commercial devices such as fuel cells and electrolyzers. A high surface area Ni foam catalyst that can sustain exceptional oxygen evolution reaction (OER) current densities of up to 4 A cm−2 in a quasi‐steady‐state within our GDE setup operating in an alkaline environment is presented. The high performance of this Ni‐based benchmark catalyst is attributed to its deposition onto a mesh‐like porous transport layer (PTL) via hydrogen‐templated electrodeposition. This forms a porous foam‐like structure that augments the mass transport of the gaseous reactants at the GDE.

The global issue for proton exchange membrane fuel cell market development is a reduction in the device cost through an increase in efficiency of the oxygen reduction reaction occurring at the cathode and an extension of the service life of the electrochemical device. Losses in the fuel cell performance are due to various degradation mechanisms in the catalytic layers taking place under conditions of high electric potential, temperature, and humidity. This review is devoted to recent advances in the field of increasing the efficiency and durability of electrocatalysts and other electrode materials by introducing structured carbon components into their composition. The main synthesis methods, physicochemical and electrochemical properties of materials, and performance of devices on their basis are presented. The main correlations between the composition and properties of structured carbon electrode materials, which can provide successful solutions to the highlighted issues, are revealed. [ABSTRACT FROM AUTHOR]

BACKGROUND: The present study investigates the in situ electrogeneration of H2O2 by the 2e− oxygen reduction reaction in an electrochemical flow cell using three commercially available cathodic electrode materials with different interfacial properties; that is, activated carbon felt (ACF), non‐activated carbon felt (NACF) and gas diffusion electrode (GDE). RESULTS: Experiments were first performed to optimize the operating parameters and to determine the yield of H2O2 electrosynthesis. The estimated maximum yield of ~40% was achieved with the NACF electrode after 30 min of operation. Furthermore, the performance of the electrodes was investigated in two scenarios, namely (i) under conditions with O2‐saturated electrolyte and (ii) under continuous air supply, to study the differences in O2 distribution within the electrode material as a function of its interfacial properties. The maximum H2O2 concentration for the first scenario was 3.86 mg L−1 after 60 min of operation, which was obtained with the NACF electrode. In contrast, in the second scenario, H2O2 electrogeneration was significantly increased for all three electrodes, with the GDE exhibiting the best performance, at 43.3 mg L−1 after 60 min of operation. CONCLUSIONS: The properties of the electrode material play a decisive role in H2O2 electrogeneration. The hydrophilicity of the electrode is very important when O2 is dissolved in the electrolyte. Hydrophobicity is preferable when gaseous O2 is applied to the electrode as a three‐phase interface is formed, which favors the transfer/penetration of O2. The pore size of the electrode is of crucial importance, as mesoporous materials facilitate the distribution of gaseous O2 in the electrode body. © 2024 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

The present work sought to investigate H2O2 generation using a gas diffusion electrode (GDE) composed of carbon with niobium oxide for levofloxacin (LEVO) degradation. Results showed that the oxide formed was Nb2O5 (crystallographic structure was confirmed by XRD; chemical composition detected by XPS), and the increase in the Nb/C ratio led to more crystalline structure and higher crystallite size. The carbon with 5% Nb2O5 presented an average particle size of 5.6 nm, and this material led to the generation of the highest amount of H2O2 (317.6 mg L−1). The C/5% Nb2O5-modified GDE was applied for the degradation of LEVO in an acid medium in the presence and absence of Fe2+ ions. Long-term experiments conducted to analyze the time required for the total removal of LEVO showed that 96% of LEVO and 66% of organic load were removed in 270 min of treatment at the current density of 100 mA cm−2. [ABSTRACT FROM AUTHOR]

[Display omitted] Electrochemical CO 2 reduction (eCO 2 R) to industrially important feedstock has received great attention, but it faces different challenges. Among them, the poor CO 2 mass transport due to low intrinsic CO 2 solubility significantly limits the rate of reduction reactions, leading to lower catalytic performance; thereby, commercially relevant current densities can't be achieved. Moreover, the poor activity and selectivity of high-cost monometallic catalysts, including Cu, Zn, Ag, and Au, undermine the efficiency of eCO 2 R. Flow-through gas diffusion electrodes (FTGDE), a newly developed class of GDEs, can potentially solve the issue of poor CO 2 mass transport because they directly feed the CO 2 to the catalyst layer. In addition, abundant surface area, porous structure, and improved triple-phase interface make them an excellent candidate for extremely high rate eCO 2 R. Antimony, a low-cost and abundant metalloid, can be effectively tuned with Cu to produce useful products such as CO, formate, and C 2 H 4 through eCO 2 R. Herein, a series of porous binary CuSb FTGDEs with different Sb compositions are fabricated for the electrocatalytic reduction of CO 2 to CO. The results show that the catalytic performance of CuSb FTGDEs improved with increasing Sb content up to a certain threshold, beyond which it started to decrease. The CuSb FTGDE with 5.4 g of antimony demonstrated higher current density (206.4 mA/cm2) and faradaic efficiency (72.82 %) at relatively lower overpotentials. Compared to gas diffusion configuration, the poor catalytic activity and selectivity achieved by CuSb FTGDE in non-gas diffusion configuration signifies the importance of improved local CO 2 concentration and improved triple-phase interface formation in GDE configuration. The several hours stable operation of CuSb FTGDEs during eCO 2 R demonstrates its potential for efficient electrocatalytic conversion applications. [ABSTRACT FROM AUTHOR]

Carbon dioxide electroreduction (CO2R) is a promising technology for mitigating industrial CO2 emissions and generating valuable chemicals using renewable energy sources. Recent advances have centered on fine‐tuning catalyst materials and their micro‐environments, stimulating interest within the CO2R community. However, testing novel catalyst materials often occurs under conditions different from those relevant to industrial applications. In this study, we explore the transferability of CO2R results obtained using Ag‐based gas diffusion electrode (GDEs) in an easy to fabricate, assemble and test zero‐gap half‐cell (ZGHC) to a zero‐gap electrolyzer (ZGE). Our investigation reveals that the transferability of results is not only influenced by the reactor design, but also partially dependent on the type of additive used in the catalyst layer of the GDE. Moreover, we show that the humidity of the CO2 is a crucial operational parameter that not only impacts the selectivity of the electrode but also influences its stability during testing in the ZGHC. These findings highlight the importance of comprehensively considering operational conditions as well as reactor designs when comparing results between the ZGHC and ZGE, presenting finally a pathway on how to minimize such differences. [ABSTRACT FROM AUTHOR]

Fe‐N‐C catalysts are a promising alternative to replace cost‐intensive Pt‐based catalysts in high temperature polymer electrolyte membrane fuel cell (HT‐PEMFC) electrodes. However, the electrode fabrication needs to be adapted for this new class of catalysts. In this study, gas diffusion electrodes (GDEs) are fabricated using a commercial Fe‐N‐C catalyst and different polytetrafluorethylene (PTFE) binder ratios, varying from 10 to 50 wt % in the catalyst layer (CL). The oxygen reduction reaction performance is investigated under HT‐PEMFC conditions (160 °C, conc. H3PO4 electrolyte) in a half‐cell setup. The acidophilic character of the Fe‐N‐C catalyst leads to intrusion of phosphoric acid electrolyte into the CL. The strength of the acid penetration depends on the PTFE content, which is visible via the contact angles. The 10 wt % PTFE GDE is less capable to withdraw product water and electrolyte and results into the lowest half‐cell performance. Higher PTFE contents counterbalance the acid drag into the CL and impede flooding. The power density at around 130 mA mgCatalyst−2 increases by 34 % from 10 to 50 wt % PTFE. [ABSTRACT FROM AUTHOR]

The use of gas diffusion electrode (GDE) based flow cell can realize industrial-scale CO2 reduction reactions (CO2RRs). Controlling local CO2 and CO intermediate diffusion plays a key role in CO2RR toward multi-carbon (C2+) products. In this work, local CO2 and CO intermediate diffusion through the catalyst layer (CL) was investigated for improving CO2RR toward C2+ products. The gas permeability tests and finite element simulation results indicated CL can balance the CO2 gas diffusion and residence time of the CO intermediate, leading to a sufficient CO concentration with a suitable CO2/H2O supply for high C2+ products. As a result, an excellent selectivity of C2+ products ~ 79% at a high current density of 400 mA·cm−2 could be obtained on the optimal 500 nm Cu CL (Cu500). This work provides a new insight into the optimization of CO2/H2O supply and local CO concentration by controlling CL for C2+ products in CO2RR flow cell. [ABSTRACT FROM AUTHOR]

The successful electrochemical reduction of CO 2 (eCO 2 R) into valuable fuels and chemicals relies on the development of low-cost, effective carbon-bonded metal catalysts. Carbon-bonded metal catalysts are crucial for efficient eCO 2 R due to their dual functionality—high electrical conductivity from carbon and catalytic activity from the metal. In this study, a facile hydrothermal method was used to synthesize carbon-derived bismuth oxide nanospheres (C-BiO x) on porous nickel foam (NF) electrodes as electrocatalysts for eCO 2 R. The eCO 2 R activity of this catalyst was evaluated in H-type cells and compared with commercially available Pd/C and Ag-nanoparticle catalysts. Our finding revealed that C-BiO x /NF exhibited a higher eCO 2 R activity (corresponding to the CO Faradaic efficiency (FE) of 16.2 % at −1 V vs. reversible hydrogen electrode (RHE) and HCOOH FE of 85.4 % at −0.7 V vs. RHE) than those of the Ag nanoparticle-based and Pd/C catalysts. Mechanistic insights from DFT-based studies further supported the enhanced catalytic activity of C-BiOx for HCOOH production over Ag catalysts. The fabricated catalyst was further utilized in a zero-gap CO 2 electrolyzer for gas-phase CO 2 reduction containing a self-supporting C-BiO x /NF gas diffusion layer (GDL). An anion exchange membrane-based CO 2 electrolyzer demonstrated a higher FE for CO formation (47.1%) with an energy efficiency (EE) of 29.5% as compared to those of a polymer electrolyte membrane-based CO 2 electrolyzer (FE: 25.2%, EE: 18.4%). Notably, the C-BiO x /NF catalyst exhibited remarkable stability (8 h) in the gas-phase GDL compared to that observed during the liquid-phase eCO 2 R. Our work provides new insights into utilizing improved catalyst designs in conjunction with flow cells for successful commercial implementation of this promising technology. Gas phase CO 2 electrolyzer with C-BiOx/NF gas diffusion layer for efficient and durable CO production. CO 2 electrolyzers are emerging as a promising route to convert CO 2 into fuel and alleviate the global worming problem. [Display omitted] • Carbon-derived bismuth oxide nanospheres (C-BiO x) on NF is fabricated. • High electrocatalytic activity and stability for eCO 2 RR are demonstrated. • Oxygen vacancies promote the transport of electrons for eCO 2 RR. • Self-standing ionomer free low loading C-BiO x /NF electrode for AEM and PEM reactors. • Demonstrated high catalytic stability during gas-phase CO 2 electrolysis on GDL. [ABSTRACT FROM AUTHOR]

The generation of "green" oxidizing agents by electrochemical synthesis opens the field for sustainable, on-demand, and on-site production, which is often based on non-critical starting materials. In this study, electrosyntheses were carried out on different cathode and anode materials. In half-cell experiments, the cathodic synthesis of peracetic acid (PAA) was investigated on gas diffusion electrodes (GDEs), reaching 22.6 mmol L-1 of PAA with a current efficiency (CE) of 7.4%. Moreover, peroxodicarbonate (PODIC®) was produced anodically on boron-doped diamond (BDD) electrodes with concentrations as high as 42.7 mmol L-1 PODIC® and a CE of 30.3%. Both cathodic and anodic processes were individually examined and improved. Finally, the half-cell reactions were combined as a proof of concept in a parallel paired electrolysis cell for the first time to achieve an increased overall CE. [ABSTRACT FROM AUTHOR]

Microbial electrosynthesis (MES) have been proven effective at reducing carbon dioxide (CO 2) and synthesizing valuable organic commodities with the aid of electrical energy. The development of highly productive MES is challenging due to low bacterial loading, low electron transfer rate, and low solubility of CO 2 , which can decrease the production of relevant chemicals and further limit the future potential of upscaling. Many innovations have been established to upscale the system including the application of gas diffusion electrodes (GDEs) in a three-chambered MES system. To date, two types of commercially available GDEs have been employed in MES: polytetrafluoroethylene (PTFE) and carbon-based GDEs. The process of bacterial adhesion on the electrolyte-facing side of the GDE is influenced by material surface properties, such as surface charge, wettability, roughness, and area. Thus, a suitable material is required to modify the aforementioned GDE surfaces. Recently, researchers have been keen on modifying bio-electrodes with conducting polymers in microbial fuel cells and MES as they show fascinating outcomes. Moreover, modifying GDEs using conducting polymers (CPs) is well-established in fuel cells but highly lacking in MES. Several modification strategies can be adopted in MES, such as the microporous layer (MPL) coating, CP MPL, and CP-based MPL. Last, the present review features possible modifications of carbon-based GDE using CPs and its challenges. [Display omitted] • Comparison of GDE and Non-GDE microbial electrosynthesis cell. • Application of PTFE-based and carbon based GDE in MES. • Factors affecting biofilm formation on electrolyte facing side of GDE. • Modification of electrolyte facing side GDE with conducting polymer. [ABSTRACT FROM AUTHOR]

Gas diffusion electrodes (GDEs) mediate the transport of reactants, products and electrons for the electrocatalytic CO2 reduction reaction (CO2RR) in membrane electrode assemblies. The random distribution of ionomer, added by the traditional physical mixing method, in the catalyst layer of GDEs affects the transport of ions and CO2. Such a phenomenon results in elevated cell voltage and decaying selectivity at high current densities. This paper describes a pre-confinement method to construct GDEs with homogeneously distributed ionomer, which enhances mass transfer locally at the active centers. The optimized GDE exhibited comparatively low cell voltages and high CO Faradaic efficiencies (FE > 90%) at a wide range of current densities. It can also operate stably for over 220 h with the cell voltage staying almost unchanged. This good performance can be preserved even with diluted CO2 feeds, which is essential for pursuing a high single-pass conversion rate. This study provides a new approach to building efficient mass transfer pathways for ions and reactants in GDEs to promote the electrocatalytic CO2RR for practical applications. [ABSTRACT FROM AUTHOR]

This paper presents a membrane electrode assembly (MEA) with a double-catalytic layered structure to improve the performance of the micro direct methanol fuel cell. The inner and outer parts of the double-catalytic layer comprise an unsupported and carbon-supported catalyst, respectively. A two-dimensional two-phase model of mass transport and electrochemical reaction is established and simulated to analyze the superiority of the double-catalytic layered structure. Simulation results show that this structure has a more uniform current density distribution and less over-potential across the catalyst layer. Methanol crossover is also reduced. Experimental results confirm that the MEA with the double-catalytic layered structure exhibits better performance than the traditional MEA. The adoption of a gas diffusion electrode as the outer catalytic layer and a catalyst-coated membrane as the inner layer of the double-catalytic layered structure can further improve the performance of the MEA. Both simulation and experimental results show the existence of an optimum number of metal loadings of the inner and outer parts of the double-catalytic layer. [ABSTRACT FROM AUTHOR]

A promising step towards a carbon-free gas diffusion electrode (CF-GDE) design for alkaline applications is shown in this work. MnO x ´s are electrodeposited on nickel foam by varying the settings, and then they were annealed at 300 °C. These CF-GDEs were characterized and compared with a commercial carbon-based GDE (GDE ref). Samples were analyzed by XRD, SEM, X-ray tomography, contact angle method, nitrogen sorption, and electrochemical methods. Electrochemical impedance spectroscopy confirmed the higher reactant transport of CF-GDEs during OER and ORR. The large pore size of the CF-GDE substrate (nickel foam) results in a high supply of catalyst sites deep inside the CF-GDE. The transport distance of gaseous O 2 is also reduced since the thin electrolyte film is at the gas bulk of the CF-GDE. The catalytic bifunctionality was additionally examined by galvanostatic measurements at 5 and 10 mA cm− 2. A promising CF-GDE exhibited 0.43 V η OER and −2.43 V η ORR at 10 mA cm−2. Lastly, long-term stability measurements of 2100 cycles at 1.5 V (OER) and −0.75 V (ORR) vs. Hg/HgO in 1 M NaOH show the carbon corrosion of GDE ref (60% current density loss) and a stable current density of CF-GDE. • Designing a bifunctional carbon-free gas diffusion electrode (CF-GDE) for alkaline applications. • The CF-GDE indicated a higher reactant supply than the carbon-based GDE. • Higher OER activity due to large substrate pores of Ni foam combined with MnO x coating. • In situ formation of NiMn layered double hydroxides increased CF-GDEs current density. [ABSTRACT FROM AUTHOR]

Presented here is an electrochemical three-electrode Gas Diffusion Electrode (GDE) cell tailored for operandoand in situ investigations of electrocatalytic processes, with a particular focus on X-ray scattering studies. The optimized cell is engineered to accommodate the minimal sample-detector distances requisite for comprehensive X-ray total scattering investigations. An in-depth understanding of catalytic processes requires their study under ‘working’ conditions. Configured as a flow-cell, the setup therefore enables the examination of electrocatalysts under high current densities and associated gas evolution phenomena, particularly pertinent for reactions like the oxygen evolution reaction (OER). Notably, its transparency simplifies cell alignment, troubleshooting, and facilitates scans through the catalyst layer, crucial for background corrections. Demonstrating its versatility, we showcase its utility through Small Angle X-ray Scattering (SAXS), X-ray Diffraction (XRD), and X-ray Pair Distribution Function (PDF) analyses of total scattering data.

Electrocatalytic CO2 reduction reaction (CO2RR) is a promising strategy to convert CO2 into fuels and building blocks for chemicals, exploiting renewable energy sources. Flow cells using gas diffusion electrodes (GDEs) instead of simple H-cells are required to achieve higher production rates. In a GDE, CO2 diffuses through a porous gas diffusion layer (GDL) and reaches the active sites located in the catalyst layer; the GDL is a crucial component that can affect the performance of the GDE. In this work, we aimed to establish the parameters of the GDL that influence the selectivity toward the different CO2 reduction products in an alkaline flow reactor. We employed commercial Cu nanoparticles as electrocatalyst and selected a range of market-available GDLs: the structure, composition, and type of cracks of the GDL greatly influence the Faradaic Efficiency (FE) of CO, H2, and ethylene (C2H4). With the emphasis on C2H4, it was found that using a crack-free GDE is essential to get higher FEC2H4. At the same time, larger and more abundant cracks are detrimental to C2H4 production and promote hydrogen evolution: for instance, the FEC2H4 varies in the wide range of 13–32%, from the highly cracked to the crack-free GDL. The presence of both sulfur and oxygen in the microporous layer (MPL) of the GDL helps shift the CO2RR selectivity toward CO. The (in)stability of the GDEs at high current density has been correlated with a change in the wetting properties of the GDE and a loss in hydrophobicity.

Abstract Carbon dioxide electroreduction (CO2R) is a promising technology for mitigating industrial CO2 emissions and generating valuable chemicals using renewable energy sources. Recent advances have centered on fine‐tuning catalyst materials and their micro‐environments, stimulating interest within the CO2R community. However, testing novel catalyst materials often occurs under conditions different from those relevant to industrial applications. In this study, we explore the transferability of CO2R results obtained using Ag‐based gas diffusion electrode (GDEs) in an easy to fabricate, assemble and test zero‐gap half‐cell (ZGHC) to a zero‐gap electrolyzer (ZGE). Our investigation reveals that the transferability of results is not only influenced by the reactor design, but also partially dependent on the type of additive used in the catalyst layer of the GDE. Moreover, we show that the humidity of the CO2 is a crucial operational parameter that not only impacts the selectivity of the electrode but also influences its stability during testing in the ZGHC. These findings highlight the importance of comprehensively considering operational conditions as well as reactor designs when comparing results between the ZGHC and ZGE, presenting finally a pathway on how to minimize such differences.

Abstract Fe‐N‐C catalysts are a promising alternative to replace cost‐intensive Pt‐based catalysts in high temperature polymer electrolyte membrane fuel cell (HT‐PEMFC) electrodes. However, the electrode fabrication needs to be adapted for this new class of catalysts. In this study, gas diffusion electrodes (GDEs) are fabricated using a commercial Fe‐N‐C catalyst and different polytetrafluorethylene (PTFE) binder ratios, varying from 10 to 50 wt % in the catalyst layer (CL). The oxygen reduction reaction performance is investigated under HT‐PEMFC conditions (160 °C, conc. H3PO4 electrolyte) in a half‐cell setup. The acidophilic character of the Fe‐N‐C catalyst leads to intrusion of phosphoric acid electrolyte into the CL. The strength of the acid penetration depends on the PTFE content, which is visible via the contact angles. The 10 wt % PTFE GDE is less capable to withdraw product water and electrolyte and results into the lowest half‐cell performance. Higher PTFE contents counterbalance the acid drag into the CL and impede flooding. The power density at around 130 mA mgCatalyst−2 increases by 34 % from 10 to 50 wt % PTFE.

The use of gas diffusion electrodes (GDEs) in microbial fuel cells (MFCs) can improve their cell performance, but tends to cause fouling. In order to allow long-term stable operation, the search for antifouling methods is necessary. Therefore, an antibacterial coating with ammonium compounds is investigated. Within the first 30 days of operation, the maximum measured power density of a GDE with antibacterial ionomer was 606 mW m−2. The GDE without an antifouling treatment could only reach a maximum of 284 mW m−2. Furthermore, there was an optimum in the loading amount with ionomer below 2.6 mg cm−2. Further investigations showed that additional aeration of the GDEs by a fan had a negative effect on their performance. Despite the higher performance, the antibacterial coating could not prevent biofilm growth at the surface of the GDE. The thickness of the biofilm was only reduced by 14–16%. However, the weight of the biofilm on the treated GDEs was 62–80% less than on a GDE without an antifouling treatment. Consequently, the coating cannot completely prevent fouling, but possibly leads to a lower density of the biofilm or prevents clogging of the pores inside the electrodes and improves their long-term stability.

This study explored the impact of solvent dielectric constant on the catalyst layer of proton exchange membrane fuel cell (PEMFC) cathodes during the oxygen reduction reaction. Electrochemical analyses were conducted at 25ºC in 2.0 M H2SO4 on electrodes that had been prepared with the same Nafion and Pt loadings, but different solvent dielectric constants for ink preparation of the catalyst layer. A Nafion loading of 0.5 mg cm-2 and Pt loading of 1 mg cm-2 were employed for all electrodes. The findings of the research revealed that the dielectric constant of the ink utilized for preparing the gas diffusion electrode reaction layer has an impact on the electrode's performance for the oxygen reduction reaction. This effect was evident in both the kinetics parameters linked to the oxygen reduction reaction and the physical characteristics of the electrode surface. In the preparation of the reaction layer, an optimal electrode performance result of 4.2 was achieved in relation to the dielectric constant.

The generation of “green” oxidizing agents by electrochemical synthesis opens the field for sustainable, on-demand, and on-site production, which is often based on non-critical starting materials. In this study, electrosyntheses were carried out on different cathode and anode materials. In half-cell experiments, the cathodic synthesis of peracetic acid (PAA) was investigated on gas diffusion electrodes (GDEs), reaching 22.6 mmol L−1 of PAA with a current efficiency (CE) of 7.4%. Moreover, peroxodicarbonate (PODIC®) was produced anodically on boron-doped diamond (BDD) electrodes with concentrations as high as 42.7 mmol L−1 PODIC® and a CE of 30.3%. Both cathodic and anodic processes were individually examined and improved. Finally, the half-cell reactions were combined as a proof of concept in a parallel paired electrolysis cell for the first time to achieve an increased overall CE.

As a carbon capture and utilization (CCU) technology, gas diffusion electrode (GDE) based electrochemical CO2 reduction reaction (eCO2RR) can convert CO2 to valuable products, such as formate and CO. However, the electrode parameters and operational conditions need to be studied and optimised to enhance the performance and reduce the net cost of the eCO2RR process before its industrial application. In this work, a machine learning algorithm, i.e., extended adaptive hybrid functions (E-AHF) is combined with a multi-physics model for the data-driven three-objective optimisation and techno-economic analysis of the GDE-based eCO2RR process. The effects of eight design variables on the product yield (PY), CO2 conversion (CR) and specific electrical energy consumption (SEEC) of the process are analysed. The results show that the R2 of the E-AHF model for the prediction of PY, CR and SEEC are all higher than 0.96, indicating the high accuracy of the developed machine learning algorithm for the prediction of the eCO2RR process. The process performance experiences a notable improvement after optimisation and is affected by a combination of eight variables, amongst which the electrolyte concentration having the most significant impact on PY and CR. The optimal trade-off single-pass PY, CR and SEEC are 3.25×10−9 kg s−1, 0.663% and 9.95 kWh kg−1 based on flow channels with 1 cm in length, respectively. The SEEC is reduced by nearly half and PY and CR are improved more than two times after optimisation. The production cost of the GDE-based eCO2RR process was approximately $378 t−1product (CO and formate), much lower than that of traditional CO2 utilisation factories ($835 t−1product). The electricity cost accounted for more than 80% of the total cost, amounting to $318 t−1, indicating that cheaper and cleaner electricity sources would further reduce the production cost of the process, which is the key to the economics of this technology.

Alkaline water electrolysis is a well-known technology for sustainable hydrogen production powered by renewable energy. The use of gas diffusion electrodes (GDEs) based on nonprecious materials eliminates the need for an anolyte cycle, leading to a cost reduction of the electrolysis process. In this work, the production of GDEs made of nickel particles and different iron precursors is investigated for the improvement of the oxygen evolution reaction. The GDE production followed an established four-step process: dispersing, spraying, hot pressing, and sintering. Physical characterization comprised the determination of the pore size distribution by capillary flow porometry and mercury porosimetry, as well as BET surface area measurements. Electrochemical characterization through linear sweep voltammetry and EIS measurements was performed in a custom half cell. The results show that the overall performance of the GDE based on low-cost iron compounds was comparable to existing GDE formulations, while improvements could be achieved regarding the overpotential in the kinetic region. Nevertheless, future investigations concerning the gas purity and long-term stability of the GDEs will be the next steps of the electrode development. [ABSTRACT FROM AUTHOR]

Aiming to advance the technical maturity of CO2 electrolysis to formic acid, various gas diffusion layers (GDLs) are investigated for their suitability as carbon‐based substrate for gas diffusion electrodes (GDEs) and their effect on the electroreduction of CO2 to formate. Particular attention lies on the elucidation for the effect of the GDL thickness, hydrophobic treatment, and presence of a microporous layer (MPL) on the GDE performance in terms of Faradaic efficiency. Based on the investigation it is found that the GDL thickness has no discernible influence on the Faradaic efficiency, while a GDE with a hydrophobic treatment of 10 % PTFE outperforms a GDE based on a GDL with 30 % PTFE. Furthermore, the presence of a MPL is found to be of marked importance to achieve relevant current densities given its effect on the focus of the catalyst layer on the GDE surface after spray coating, the wetting, and the electrical conductivity. [ABSTRACT FROM AUTHOR]

The global issue for proton exchange membrane fuel cell market development is a reduction in the device cost through an increase in efficiency of the oxygen reduction reaction occurring at the cathode and an extension of the service life of the electrochemical device. Losses in the fuel cell performance are due to various degradation mechanisms in the catalytic layers taking place under conditions of high electric potential, temperature, and humidity. This review is devoted to recent advances in the field of increasing the efficiency and durability of electrocatalysts and other electrode materials by introducing structured carbon components into their composition. The main synthesis methods, physicochemical and electrochemical properties of materials, and performance of devices on their basis are presented. The main correlations between the composition and properties of structured carbon electrode materials, which can provide successful solutions to the highlighted issues, are revealed.

The industrial adoption of microbial electrosynthesis (MES) is hindered by high overpotentials deriving from low electrolyte conductivity and inefficient cell designs. In this study, a mixed microbial consortium originating from an anaerobic digester operated under saline conditions (∼13 g L−1 NaCl) was adapted for acetate production from bicarbonate in galvanostatic (0.25 mA cm−2) H-type cells at 5, 10, 15, or 20 g L−1 NaCl concentration. The acetogenic communities were successfully enriched only at 5 and 10 g L−1 NaCl, revealing an inhibitory threshold of about 6 g L−1 Na+. The enriched planktonic communities were then used as inoculum for 3D printed, three-chamber cells equipped with a gas diffusion biocathode. The cells were fed with CO2 gas and operated galvanostatically (0.25 or 1.00 mA cm−2). The highest production rate of 55.4 g m−2 d−1 (0.89 g L−1 d−1), with 82.4% Coulombic efficiency, was obtained at 5 g L−1 NaCl concentration and 1 mA cm−2 applied current, achieving an average acetate production of 44.7 kg MWh−1. Scanning electron microscopy and 16S rRNA sequencing analysis confirmed the formation of a cathodic biofilm dominated by Acetobacterium sp. Finally, three 3D printed cells were hydraulically connected in series to simulate an MES stack, achieving three-fold production rates than with the single cell at 0.25 mA cm−2. This confirms that three-chamber MES cells are an efficient and scalable technology for CO2 bio-electro recycling to acetate and that moderate saline conditions (5 g L−1 NaCl) can help reduce their power demand while preserving the activity of acetogens.

Abstract Aiming to advance the technical maturity of CO2 electrolysis to formic acid, various gas diffusion layers (GDLs) are investigated for their suitability as carbon‐based substrate for gas diffusion electrodes (GDEs) and their effect on the electroreduction of CO2 to formate. Particular attention lies on the elucidation for the effect of the GDL thickness, hydrophobic treatment, and presence of a microporous layer (MPL) on the GDE performance in terms of Faradaic efficiency. Based on the investigation it is found that the GDL thickness has no discernible influence on the Faradaic efficiency, while a GDE with a hydrophobic treatment of 10 % PTFE outperforms a GDE based on a GDL with 30 % PTFE. Furthermore, the presence of a MPL is found to be of marked importance to achieve relevant current densities given its effect on the focus of the catalyst layer on the GDE surface after spray coating, the wetting, and the electrical conductivity.

The transition of today's fossil fuel based chemical industry toward sustainable production requires improvement of established production processes as well as development of new sustainable and bio‐based synthesis routes within a circular economy. Thereby, the combination of electrochemical and biotechnological advantages in such routes represents one important keystone. For the electrochemical generation of reactants from gaseous substrates such as O2 or CO2, gas diffusion electrodes (GDE) represent the electrodes of choice since they overcome solubility‐based mass transport limitations. Within this article, we illustrate the architecture, function principle and fabrication of GDE. We highlight the application of GDE for conversion of CO2 using abiotic catalysts for subsequent biosynthesis as well as the application of microbial catalysts at GDE for CO2 conversion. The reduction of oxygen at GDE is summarized for the application of oxygen depolarized cathodes in microbial fuel cells and generation of H2O2 to drive enzymatic reactions. Finally, engineering aspects such as scale‐up and the modeling of GDE‐based processes are described. This review presents an update on the application of GDE in bio‐based production systems and emphasizes their large potential for sustainable development of new pathways in bioeconomy. [ABSTRACT FROM AUTHOR]

This study explored the impact of solvent dielectric constant on the catalyst layer of proton exchange membrane fuel cell (PEMFC) cathodes during the oxygen reduction reaction. Electrochemical analyses were conducted at 25°C in 2.0 M H2SO4 on electrodes that had been prepared with the same Nafion and Pt loadings, but with various solvent dielectric constants for ink preparation of the catalyst layer. A Nafion loading of 0.5 mg cm-2 and Pt loading of 1 mg cm-2 were employed for all electrodes. The findings of the research revealed that the dielectric constant of the ink utilized for preparing the gas diffusion electrode reaction layer has an impact on the electrode's performance for the oxygen reduction reaction. This effect was evident in both the kinetics parameters linked to the oxygen reduction reaction and the physical characteristics of the electrode surface. In the preparation of the reaction layer, an optimal electrode performance result of 4.2 was achieved in relation to the dielectric constant. [ABSTRACT FROM AUTHOR]

The rational design of high-performance electrocatalysts requires a detailed understanding of dynamic changes in catalyst properties, including oxidation states, surface area, and morphology under realistic working conditions. Oxide-derived Cu catalysts exhibit a remarkable selectivity toward multicarbon products for the electrochemical CO reduction reaction (CORR), but the exact role of the oxide remains elusive for explaining the performance enhancements. Here, we used operando X-ray absorption spectroscopy (XAS) coupled with simultaneous measurements of the catalyst activity and selectivity by gas chromatography (GC) to study the relationship between oxidation states of Cu-based catalysts and the activity for ethylene (C2H4) production in a CO gas-fed cell. By utilizing a custom-built XAS cell, oxidation states of Cu catalysts can be probed in device-relevant settings and under high current densities (>80 mA cm-2) for the CORR. By employing an electrochemical oxidation process, we found that the Cu oxidation states and specific ion species do not correlate with C2H4 production. The difference in the CORR activity is also investigated in relation to electrochemical surface area (ECSA) changes. While the hydrogen evolution reaction (HER) activity is positively correlated to the ECSA changes, the increased C2H4 activity is not proportional to the ECSA. Ex situ characterization from microscopic techniques suggests that the changes in the C2H4 activity and selectivity may arise from a morphological transformation that evolves into a more active structure. These comprehensive results give rise to the development of a cell regeneration method that can restore the performance of the Cu catalyst without cell disassembly. Our study establishes a basis for the rational design of highly active electrocatalysts for broad-range reactions in a gas-fed device.

Using electrolysis systems to degrade organics in wastewater encourages this technique to remove micropollutants (MPs) in different types of water. In this work, a cell consisting of an anode as a boron-doped diamond (BDD) electrode combined with a gas diffusion (GDE) cathode without a separator showed that MPs degradation can be effectively achieved. Investigating different operating parameters, it was stated that applying a low current density (2 mA/cm2) and setting the Reynolds number of the electrolyte flow through the cell at the laminar range raised the treatment time by 3-fold at the same energy demand. This arrangement increased the MPs removal. Some substances like diclofenac were removed up to 84% at a longer treatment time of 180 min coupled with an increase in energy demand. The results at the mentioned parameters indicated an adequate generation rate of radicals needed to remove MPs and the oxidation reactions were promoted. The results show high potential to the investigated electrolysis system in removing MPs in wastewater under considering the need for further reduction of the energy demand. HIGHLIGHTS Investigaton of innovative electrolysis system to remove water micropollutants.; Explanation and controlling the system reactions towards the highest yield.; Confirmation of removal possibility at different operating parameters.; Studying how the operating parameters affect the treatment process effectivity.; Determination of the best system settings to get the best removal efficiency.;

Abstract Electrochemical CO2 conversion has been raised as a promising solution for building a carbon‐neutral economy under today's circumstances of increasing energy shortages and air pollution from human activities. Research on electrochemical CO2 reduction reaction (CO2RR) is gradually entering a pilot‐scale stage. The use of device‐level CO2 electrolysis in the production of value‐added chemicals and fuels at a high production rate and selectivity is highly required to make the technology economical and sustainable. With more exploration toward device‐level performance optimization, it gradually becomes clear that electrode engineering on structures, surface properties, active site distribution, and density, as well as the electrode–electrolyte interface, is more critical than the intrinsic activity of catalytic sites. Taking this into account, this review focuses on interpreting the design principles in aspects with the aim of enhancing the CO2RR toward a specific product yield and production rate. This mini‐review summarizes the advances in this dynamic field in the most recent 5 years, including the fabrication of porous gas diffusion electrodes, and self‐supporting electrodes, establishment of tandem or cascade electrode function, as well as tuning of interfacial cation buffering and wettability, and analyze the trends in the future scientific and technological development of device‐level CO2 electrolysis. Hopefully, this mini‐review could provide some insights into the opportunities in the next‐generation electrode design for the industrial carbon cycle.

The uniform coating of catalytic materials on the electrode surface is essential for improving the performance of electrochemical reactions. In this study, the electrostatic spray coating technique is used to deposit Molybdenum disulfide (MoS 2) particles on carbon electrodes and examine the electrochemical hydrogen evolution reaction (HER) performance in a 0.1 M H 2 SO 4 electrolyte. The experimental results reveal that the electrostatic spray coating method achieves a more uniform coating MoS 2 catalyst particles on the carbon fiber substrate. It provides good adhesion for electrocatalyst binding on the carbon paper electrodes. During HER analysis, a 25% higher current density is obtained from the electrostatic spray-coated electrodes compared to the manual spray-coated electrode at a potential of 0.95 V. Electrochemical impedance spectroscopy, and electrochemical surface area measurements indicate the superior electrochemical characteristics of the electrostatic spray-coated electrode. The faradaic efficiency of the electrostatic spray-coated electrode is close to 100% at a high applied potential of −1.6 V with a 0.0059 L volume of hydrogen generation. Moreover, chronoamperometric measurements demonstrate the excellent durability of the electrostatic spray-coated carbon electrodes. This study suggests that the facile electrostatic spray method is efficient for coating electrodes with high uniformity and good adhesion for various electrochemical applications. • The parametric study and its results verify the relevant coating method for HER process. • The electrostatic spray is the efficient method, exhibits high uniformity and good adhesion. • The electrostatic spray-coated electrodes delivered higher current density than manual spray-coated electrodes. • The electrostatic spray provides 100% faradaic efficiency at −1.6 V. [ABSTRACT FROM AUTHOR]

[Display omitted] Hydrogen peroxide (H 2 O 2) is a versatile and environmentally-friendly oxidant with widespread industrial applications. In recent years, electrochemical production of H 2 O 2 through the two-electron oxygen reduction reaction (ORR) pathway has been considered a promising alternative to the energy-intensive anthraquinone process. Among various electrocatalysts proposed for electrochemical generation of H 2 O 2 , metal-free carbon-based materials have attracted significant attention due to their low cost and large abundance. In this review, recent progress made in different types of metal-free carbon-based catalysts is presented. The fundamental aspects of the ORR mechanism and methodologies of ORR performance evaluation are introduced. Different metal-free electrocatalysts are then reviewed based on their dimensions, including three-dimensional, two-dimensional, one-dimensional, and zero-dimensional (3D, 2D, 1D, and 0D, respectively) catalysts. Various strategies, such as heteroatom doping, structural engineering, and defect engineering are examined for their role in enhancing catalytic efficiency. Furthermore, surface and interfacial engineering for achieving high H 2 O 2 production is discussed. Lastly, challenges and opportunities in this field are proposed to guide future research toward the rational design of metal-free catalysts for the electrochemical production of H 2 O 2. [ABSTRACT FROM AUTHOR]