The combination of density functional theory (DFT), machine learning, descriptor-based analysis, and computational hydrogen electrode is pivotal in discovering novel classed of active catalysts for oxygen reduction reaction (ORR).

Hydrogen peroxide (H2O2) stands as one of the foremost utilized oxidizing agents in modern times. The established method for its production involves the intricate and costly anthraquinone process. However, a promising alternative pathway is the electrochemical hydrogen peroxide production, accomplished through the oxygen reduction reaction via a 2-electron pathway. This method not only simplifies the production process but also upholds environmental sustainability, especially when compared to the conventional anthraquinone method. In this review paper, recent works from the literature focusing on the 2-electron oxygen reduction reaction promoted by carbon electrocatalysts are summarized. The practical applications of these materials in the treatment of effluents contaminated with different pollutants (drugs, dyes, pesticides, and herbicides) are presented. Water treatment aiming to address these issues can be achieved through advanced oxidation electrochemical processes such as electro-Fenton, solar-electro-Fenton, and photo-electro-Fenton. These processes are discussed in detail in this work and the possible radicals that degrade the pollutants in each case are highlighted. The review broadens its scope to encompass contemporary computational simulations focused on the 2-electron oxygen reduction reaction, employing different models to describe carbon-based electrocatalysts. Finally, perspectives and future challenges in the area of carbon-based electrocatalysts for H2O2 electrogeneration are discussed. This review paper presents a forward-oriented viewpoint of present innovations and pragmatic implementations, delineating forthcoming challenges and prospects of this ever-evolving field.

With the global transition towards cleaner energy and sustainable processes, the demand for efficient catalysts, especially for the oxygen reduction reaction, has gained attention from the scientific community. This research work investigates cerium-doped graphene-based materials as catalysts for this process with density functional theory calculations. The electrochemical performance of Ce-doped graphene was assessed within the computation hydrogen electrode framework. Our findings reveal that Ce doping, especially when synergized with an oxygen atom, shows improved catalytic activity and selectivity. For instance, Ce doping in combination with an oxygen atom, located near a border, can be selective for the 2-electron pathway. Overall, the combination of Ce doping with structural defects and oxygenated functions lowers the reaction free energies for the oxygen reduction compared to pure graphene, and consequently, might improve the catalytic activity. This research sheds light from a computational perspective on Ce-doped carbon materials as a sustainable alternative to traditional costly metal-based catalysts, offering promising prospects for green energy technologies and electrochemical applications.

The oxygen reduction reaction (ORR) plays a pivotal role in clean energy generation and sustainable chemical production, particularly in the synthesis of hydrogen peroxide (H2O2). In this study, WO3/Vulcan-XC72 electrocatalysts have been synthesized and characterized for ORR applications. We assessed the ratio of WO3 to Vulcan-XC72 and investigated the impact of electrolytes pH (covering acidic and alkaline media) on the ORR process. The results revealed that WO3 with a monoclinic crystalline phase and nanoflower-like morphology was successfully synthesized, and confirmed an improvement in surface properties, with an increase in hydrophilicity and superficial oxygenated species. Electrochemical studies showed that WO3/C was the most selective for H2O2 electrogeneration, compared to pure Vulcan-XC72, in both acidic and alkaline media. These results indicate that the ORR on the WO3/C electrocatalyst surface has a pH-dependent mechanism. Using WO3/C GDEs, an accumulation of 862mgL-1 of H2O2 was achieved after 120min of electrolysis at 100mAcm-2. The higher selectivity of WO3/C could be related to the presence of more oxygen functional acid species on the catalyst surface and increased hydrophilicity compared to pure Vulcan, as well as a synergistic effect of the WO3 nanoflowers in ORR, confirmed by theoretical calculations. The results reveal that WO3/Vulcan is a promising catalyst for H2O2 electrogeneration via the ORR.

The present work investigates the catalytic activity of NaNbO3 microcubes decorated with CeO2 nanorods on carbon (1 %, 3 %, 5 %, and 10 % w/w) for H2O2 electrogeneration. The crystalline phases and the morphology of the materials were identified with scanning electron microscopy, transmission electron microscopy, X‐ray diffraction and X-ray Photoelectronic spectroscopy. Contact angle measurements were performed to characterize the hydrophilicity of each material. The H2O2 electrogeneration was assessed by oxygen reduction reaction using the rotating ring-disk electrode technique. Electrochemical characterization results shown an enhancement on the H2O2 electrogeneration by NaNbO3 @CeO2/C-based materials compared to what was obtained with pure Vulcan XC72. The 1 % NaNbO3 @CeO2/C electrocatalyst presented the lower starting potential for the ORR and a 2.3 electron transfer, favoring the 2-electron mechanism and providing a higher H2O2 electrogeneration rate. Also, the enhancement of oxygen-containing functional groups showed the potential to comprehensively tune properties and optimize active sites and, consequently, increases the H2O2 electrogeneration. Density functional theory calculations indicated that NaNbO3 and CeO2 surfaces have a similar low theoretical overpotential for this reaction and that CeO2 improves the catalyst facilitating the electron transfer. These results indicate that NaNbO3 @CeO2/C-based electrocatalysts are promising materials for in situ H2O2 electrogeneration.

Hydrogen peroxide (H2O2) is a green oxidant, widely used in industry. To turn its synthesis green, research focused on the development of efficient catalysts for the two-electron oxygen reduction reaction (2e-ORR) to produce H2O2 from water and molecular oxygen. Despite recent progress, electrolyte effects of the electrochemical H2O2 production have remained little understood. We report a significant effect of alkali metal cations (AMCs) on the electrocatalytic H2O2 production on carbon catalysts in acidic environments. The presence of AMCs at the electrified carbon interface shift the half wave potential of the 2e-ORR from -0.48 V to -0.22 VRHE. This cationic induced enhancement effect exhibits a uniquely sensitive on/off switching behaviour depending on the voltammetric protocol. Voltammetric and direct in situ X-ray photoemission spectroscopic evidence is presented that supports a controlling role of the potential of zero charge (PZC) of the catalytic enhancement. Depending whether the electrode potential is kept cathodic or even just briefly reaches values anodic of the PZC, AMCs accumulate at the electrified interface and enhance the 2e-ORR or get repelled away from it, respectively. Density functional theory calculations associate the enhancement by the stabilization of the *OOH key intermediate. Based on this finding, we developed a refined reaction mechanism for the H2O2 production in presence of AMCs.

Different facets of ceria exhibit activities for the entire spectrum of oxygen electrochemistry.

Alkaline direct liquid fuel cells (ADLFC) have recently received increasing attention as they reduce the use of precious metals in electrocatalysts, e.g., platinum, which drastically reduces the cost of large-scale application of direct liquid fuel cells. This review article points out the main performance, challenges, advances and per-spectives in the anode, cathode, support materials and membranes applied to the ADFLC. In addition, an over-view of the fuels studied in ADFLC is reviewed. Additionally, the prospect of large-scale employment of this device as the application possibilities of this technology is reported. Thus, here we have the current state of the art related to progress in performance, stability, applicability, and findings of ADLFC through new materi-als, operating conditions, and set-up addressed in the recent years. Therefore, this review article has great potential for next-generation progress in ADLFC.

In recent years, there has been an increasingly growing interest regarding the use of electrochemical advanced oxidation processes (EAOPs) which are considered highly promising alternative treatment techniques for addressing environmental issues related to pollutants of emerging concern. In EAOPs, electrogenerated oxidizing agents, such as hydroxyl radical (HO•), can react non-selectively with a wide range of organic compounds, degrading and mineralizing their structures to unharmful molecules like CO2, H2O, and inorganic ions. To this date, a broad spectrum of advanced electrocatalysts have been developed and applied for the treatment of compounds of interest in different matrices, specifically aiming at enhancing the degradation performance. New combined methods have also been employed as alternative treatment techniques targeted at circumventing the major obstacles encountered in Fenton-based processes, such as high costs and energy consumption, which still contribute significantly toward inhibiting the large-scale application of these processes. First, some fundamental aspects of EAOPs will be presented. Further, we will provide an overview of electrode materials which have been recently developed and reported in the literature, highlighting different anode and cathode structures employed in EAOPs, their main advantages and disadvantages, as well as their contribution to the performance of the treatment processes. The influence of operating parameters, such as initial concentrations, pH effect, temperature, supporting electrolyte, and radiation source, on the treatment processes were also studied. Finally, hybrid techniques which have been reported in the literature and critically assess the most recent techniques used for evaluating the degradation efficiency of the treatment processes.

The 2-electron pathway of the oxygen reduction reaction is an unwanted process in the development of fuel cells. In contrast, it has gained the scientific community's attention due to its importance as a promising way of removing emergent pollutants and endocrine disruptors from water bodies and a more sustainable alternative for large-scale commercial hydrogen peroxide production. Cerium oxide has shown remarkable potential and selectivity experimentally for this mechanism, and its possible applications, exceeding the previous reference materials. In this work, we studied the 2-electron pathway for oxygen reduction on different ceria-cleaving directions (100), (110), (221), and (331) by first principles methods based on density functional theory. Our results show that the (100) surface is the most favorable for reduction, with the (331) crystallographic plane also showing potential for good catalytic activity. This fact could be essential for designing new nanostructures, with higher portions of those planes exposed, for higher catalytic activity.

The two-electron pathway of the oxygen reduction reaction has been gaining attention from the scientific community due to its capability of forming radical hydroxyl. In addition, it is a promising way of removing emergent pollutants, like dyes, pharmaceuticals, hormones, pesticides, and endocrine disruptors from water bodies, a very serious problem that currently challenges scientists and grows at a global scale. Theoretical calculations have already guided, over the last decade, the development of better catalysts for the oxygen reduction reaction. However, this mechanism had usually been, until recently, taken as an unwanted process since the preferred route for energy generation and the main focus of these studies is the four-electron pathway. This review summarizes the recent progress on computational calculations from the hydrogen peroxide generation process point of view, specifically focused on carbon-based materials.