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Although noble-metal based materials (IrO2 and RuO2) are regarded state-of-the-art catalysts for oxygen evolution reaction (OER), their high price, long-term instability, and scarcity have fueled the search for alternative materials that are relatively cheaper and highly abundant in nature and which can be used for the development of electrolyzers that are suitable for hydrogen production. The present work reports the development and application of a new hybrid catalyst derived from the thermal treatment of a mixture of graphene nanoribbons (GNR) and nickel pyrophosphate (β-Ni2P2O7); the proposed hybrid material was found to present remarkably improved properties which include easy charge transfer, high electroactive surface area, high activity, and effective resistance to corrosion in OER in alkaline medium. The combination of highly dispersed β-Ni2P2O7-30 wt% in direct contact with GNR-70 wt%, coupled with the application of thermal treatment – which ensured some enrichment of Ni in the GNiPy350N catalyst, contributed toward the production of an efficient material with excellent and stable OER activity in alkaline conditions. Compared to the state-of-the-art IrO2 (300 mV), the GNiPy350N catalyst required an overpotential of approximately 320 mV to reach the current density of 10 mA cm−2 when immobilized on carbon paper electrode.

Electrocatalytic production of H

Catalysis is inherently driven by the interaction of reactants, intermediates and formed products with the catalyst's surface. In order to reach the desired transition state and to overcome the kinetic barrier, elevated temperatures or electrical potentials are employed to increase the rate of reaction. Despite immense efforts in the last decades, research in thermo- and electrocatalysis has often preceded in isolation, even for similar reactions. Conceptually, any heterogeneous surface process that involves changes in oxidation states, redox processes, adsorption of charged species (even as spectators) or heterolytic cleavage of small molecules should be thought of as having parallels with electrochemical processes occurring at electrified interfaces. Herein, we compare current trends in thermo- and electrocatalysis and elaborate on the commonalities and differences between both research fields, with a specific focus on the production of hydrogen peroxide as case study. We hope that interlinking both fields will be inspiring and thought-provoking, eventually creating synergies and leverage towards more efficient decentralized chemical conversion processes.

Boron-doped diamond (BDD) electrodes are regarded as the most promising catalytic materials that are highly efficient and suitable for application in advanced electrochemical oxidation processes targeted at the removal of recalcitrant contaminants in different water matrices. Improving the synthesis of these electrodes through the enhancement of their morphology, structure and stability has become the goal of the material scientists. The present work reports the use of an ultranano-diamond electrode with a highly porous structure (B-UNCD

The present work investigates the electrocatalytic performance of two different morphologies of boron doped-diamond film electrode (microcrystalline diamond - MCD, and nanocrystalline diamond - NCD) used in electrochemical oxidation for the removal of the antibiotic ciprofloxacin (CIP). A thorough study was conducted regarding the formation of the MCD and NCD films through the adjustment of methane in CH4/H2 gas mixture, and the two films were compared in terms of crystalline structure, apparent doping level, and electrochemical properties. The physicochemical results showed that the NCD film had higher sp2 carbon content and greater doping level; this contributed to improvements in its surface roughness, as well as its specific capacitance and charge transfer, which consequently enhanced its electrocatalytic activity in comparison with the MCD. The results obtained from CIP removal and mineralization assays performed in sulfate medium also showed that the NCD was more efficient than the MCD under all the current densities investigated. The effects of CIP concentration and the evolution of the final by-products, including short-chain carboxylic acids and inorganic ions, were also investigated. The electrochemical performance of the NCD was evaluated in different aqueous matrices, including chloride medium, real wastewater and simulated urine. The application of the NCD led to complete or almost complete CIP degradation, regardless of the medium employed. The kinetic constant rates obtained under the different media investigated were as follows: synthetic urine (0.0416 min−1 – R2 = 0.991)

There has been a huge debate in the literature over the past few years regarding the groups (C, O, and N groups and their quantities) involved in oxygen reduction reaction on metal-free carbonaceou...

Oxygen reduction reaction (ORR) is greatly affected by the morphology as well as the elemental composition of the nitrogen-doped carbon-based electrocatalysts. Thus, this work focuses on: (i) nitrogen doping of different graphene-based materials (two-dimensional materials: chemically converted graphene, graphene oxide, and commercially available graphene, and one-dimensional material: graphene nanoribbons) that differ from each other by morphology as well as elemental composition and (ii) studying the ORR performance of these N-doped carbonaceous catalysts in alkaline medium. The nitrogen doping is achieved by low-cost synthetic method based on hydrothermal treatment at mild conditions. The results indicate that: (i) nitrogen doping is dependent on the carbonaceous substrate used and (ii) these N-doped graphene-based catalysts vary drastically by the electrocatalytic activity for ORR as well as the selectivity for HO2− and OH− production in alkaline medium. Roughly, predominantly HO 2 − was produced on two-dimensional graphene-based catalysts enriched with low nitrogen content (0.9–1.4 at.%) and mostly OH− was formed on graphene nanoribbons as one-dimensional catalyst containing low amount of nitrogen (2.1 at.%). This work is valuable for giving further insights into the ORR performance on N-doped graphene-based nanocarbons.

Hydrogen peroxide is considered one of the most important commodity chemicals worldwide but its main production method, the anthraquinone process, poses serious logistical, environmental and safety challenges. Electrocatalytic synthesis through the reduction of molecular oxygen is a promising H2O2 production route. However, the reduction of molecular oxygen is kinetically hindered and stable electrocatalysts with a high activity and selectivity towards the 2-electron transfer reaction are needed. In this work, we evaluated the influence of chloride on catalysts with low palladium loadings on the ORR selectivity towards H2O2. We report the factors and dynamics that influence H2O2 production and highlight synthesis strategies to obtain close to 100% selectivity. By probing the electrode surface after various degradation cycles, we evaluate the role of adsorbing species and the catalysts oxidation states on the hydrogen peroxide selectivity. We systematically modified the catalyst synthesis using different Pd-precursors that were reduced and supported on high surface area graphene nanoribbons. Identical location transmission electron microscopy was used to probe catalyst dynamics during reaction and the activities and selectivities were measured by a rotating ring disk electrode. We probe the potential boundary conditions that lead to catalyst degradation during accelerated stress tests and potentiostatic polarisation and demonstrate how the catalytically active surface can be revived after degradation. The obtained insights can be used as guideline for the development of active, selective and stable catalysts with low noble metal loadings.

In order to enhance hydrogen peroxide (H2O2) electrogeneration, a catalyst based on less than 1 wt% of Pd nanoparticles dispersed onto commercially available Printex L6 carbon black (PCL6) is proposed and synthetized. The material was characterized by physico-chemical and electroanalytical methods, demonstrating high activity with a 320 mV lower onset potential compared to pristine PCL6 and high stability after 5000 potential cycles. Its performance places it among the most efficient bi- and monometallic electrocatalysts for H2O2 production. When testing the accumulation of H2O2, a 1.69-fold molar increase was observed for Pd1%/PCL6 compared to PCL6. Different electrochemical advanced oxidation processes based on H2O2 generation have been performed to oxidize and remove pollutants as exemplarily shown on methyl paraben in Na2SO4 solution as model pollutant. A boron-doped diamond electrode was used as anode while Pd1%/PCL6 was tested in a rotating ring disk electrode (RRDE) and gas diffusion setup. Pollutant degradation followed a pseudo-first-order reaction kinetic in the following order: anodic oxidation along with H2O2 generation (AO-H2O2)

A successful market introduction of electrocatalytically produced hydrogen peroxide (H2O2) requires catalysts that are highly selective, active, and economically suitable. Here, we present important insights into tuning the selectivity toward H2O2 and elaborate on the opportunities opened for high catalytic performance. Especially the metal loading, the accompanied interparticle distance, and catalyst–support interaction were identified as key contributors for high selectivity and activity. We focused on the design of model catalysts with different Pd loadings and distinct interparticle distances and their dependency on the selectivity toward H2O2. The gained understandings can be used as guidelines for the development of highly active and selective catalysts while simultaneously reducing the noble metal loading and the associated costs.

This paper describes the synthesis and structural characterization of a novel, cheap and simple CoII complex (CoII(L)2Cl2) based on the 1,3,5-trisubstituted-pyrazoline ligand along with the electrochemical production of metal–organic electroactive films derived from this new complex. These systems were applied as electrocatalysts for hydrogen production (ACN/ACA or ACN/TFA medium) where both materials presented high performance toward hydrogen evolution. Compared to the CoII complex, the electroactive films exhibited significant electroactivity toward hydrogen evolution, presenting a remarkable TOF for H2 production (312 900 s−1, corrected by Faraday efficiency) in the presence of TFA. In addition, the generated metal–organic film showed high stability toward the electrocatalytic hydrogen production, supporting at least 1000 cycles at 20 mV s−1 in the large potential range investigated, as well as good performance and stability in the presence of 0.5 M H2SO4. Relevant insights into the mechanistic details and the role played by the CoII complex and the films during the catalytic hydrogen production are also discussed in light of the structural features and electrochemical experiments.

Made available in DSpace on 2021-06-25T11:18:23Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-08-01 The photoelectrocatalysis (PEC) technique was applied in CO2 reduction using different proportions of Cu, Pd, and Pt supported on graphene nanoribbons (GNR) and deposited on the surfaces of TiO2 nanotubes. Altogether, nine combinations of TiO2-NT/GNR-metal were assembled, although only three of them efficiently promoted the generation of methanol and ethanol in high quantities. Comparison with the photocatalysis, photolysis, and electrocatalysis techniques showed the extremely high efficiency of PEC, which enabled production of methanol and ethanol at levels around 19.2-fold and 44.4-fold higher, respectively, than photocatalysis, the second most efficient technique. The presence of metallic nanoparticles in the system facilitated CO2 reduction due to the trapping of the photogenerated electrons, prolonging their lifetime, lowering the reaction energy barrier for CO2 reduction, and provided active intermediates. Therefore, the assembly of these materials containing low amounts of metals is highly promising, since it can assist in alleviating environmental problems caused by CO2 emissions, while at the same time enabling the energetically efficient generation of compounds of commercial value. Institute of Chemistry Federal University of Mato Grosso Do sul, Av. Senador Filinto Muller, 1555, CP 549 São Carlos Institute of Chemistry University of São Paulo, Av. Trabalhador São-Carlense 400 São Paulo State University (UNESP) Institute of Chemistry Nuclear and Energy Research Institute IPEN-CNEN/SP São Paulo State University (UNESP) Institute of Chemistry

Robust electrocatalysts toward the resourceful and sustainable generation of hydrogen by splitting of water via electrocatalytic hydrogen evolution reaction (HER) are a prerequisite to realize high-efficiency energy research. Highly electroactive catalysts for hydrogen production with ultralow loading of platinum (Pt) have been under exhaustive exploration to make them cutting-edge and cost-effectively reasonable for water splitting. Herein, we report the synthesis of hierarchically structured nickel pyrophosphate (beta-Ni2P2O7) by a precipitation method and nickel phosphate (Ni-3(PO4)(2)) by two different synthetic routes, namely, simple cost-effective precipitation and solution combustion processes. Thereafter, Pt-decorated nickel pyrophosphate and nickel phosphate (beta-Ni2P2O7/Pt and Ni-3(PO4)(2)/Pt) were prepared by using potassium hexachloroplatinate and ascorbic acid. The fabricated novel nickel pyrophosphate and nickel phosphate/Pt materials were utilized as potential and affordable electrocatalysts for HER by water splitting. The detailed electrochemical studies revealed that the beta-Ni2P2O7/Pt (1 mu g.cm(-2) Pt) electrocatalyst showed excellent electrocatalytic performances for HER in acidic solution with an overpotential of 28 mV at -10 mA.cm(-2), a Tafel slope of 32 mV.dec, and an exchange current density (j(0)) of -1.31 mA.cm(-2), which were close to the values obtained using the Vulcan/Pt (8.0 mu g.cm(-2) Pt), commercial benchmarking electrocatalyst with eight times higher Pt amount. Furthermore, the beta-Ni2P2O7/Pt electrocatalyst maintains an excellent stability for over -0.1 V versus RHE for 12 days, keeping j(0) equal after the stability test (-1.28 mA cm(-2)). Very well-distributed Pt NPs inside the cages on the beta-Ni2P2O7 structure with a crystalline pattern of 0.67 nm distance to the Ni2P2O7/Pt electrocatalyst, helping the Volmer-Tafel mechanism with the Tafel reaction as a major rate-limiting step, help to liberate very fast the Pt sites after HER. The high electrocatalytic performance and remarkable durability showed the beta-Ni2P2O7/Pt material to be a promising cost-effective electrocatalyst for hydrogen production.

This short review presents a critical overview of the most recent works published in the literature related to the use of electrochemical advanced oxidation processes (EAOPs) for the treatment of antibiotics present in synthetic and real wastewaters. The first section focuses on novelties within the traditional EAOPs, including electrochemical oxidation and electrochemical Fenton-based processes. The second section is devoted to new electrochemical technologies, including heterogeneous electro-Fenton, electrochemically activated persulfate processes, and combined processes. Future perspectives about these processes are also presented to aid the continuous evolution of research in the area.

The inefficiency of conventional water treatment methods in the treatment of recalcitrant herbicides has led to the search for new, efficient and eco-friendly mechanisms for degrading these organic pollutants. Electrochemical advanced oxidation processes (EAOP) have emerged as a promising alternative due to their high degree of efficiency in degrading organic pollutants. This work investigates the removal of Tebuthiuron (TBH) in synthetic and real wastewater using different EAOPs in a flow-by reactor. The degradation/mineralization experiments were performed using boron-doped diamond electrode as anode and gas-diffusion electrode (GDE) as cathode for the in situ electrogeneration of hydrogen peroxide (H2O2). For the analysis conducted in synthetic medium, TBH degradation was found to fit well in a pseudo-first-order kinetic reaction with increasing k1 values according to the following order of efficiency: anodic oxidation (AO, 3.1 × 10−5 s−1)

Pt nanoclusters with Pt porous dendritic structures on top (high porosity materials) were electrodeposited at a low overpotential onto glassy carbon (GC) electrodes modified with graphite (GR), multiwalled carbon nanotubes (MWCNT), graphene oxide (GO), graphene oxide nanoribbons (GONR), chemically converted graphene (CCG), and graphene nanoribbons (GNR). The electrochemical profiles of these materials were investigated using cyclic voltammetry and microgravimetry (electrochemical quartz microbalance). Their electrocatalytic activity towards the oxygen-reduction reaction (ORR) was studied employing hydrodynamic cyclic voltammetry. Physical characterization of the samples was based on transmission electron microscopy (TEM), scanning electron microscope (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray microanalysis (EDX). Pt electrocatalysts electrodeposited onto CCG and GNR exhibited high electrocatalytic activity towards ORR when compared with commercial Pt (10 wt.%) on carbon and high stability after 10 000 potential scans, suggesting the possibility of applying these catalysts to acid fuel cells—viable even in economic terms, as very low amounts of finely dispersed Pt per cm 2 onto thin CCG or GNR films were required to produce the electrocatalysts. GC electrodes modified with Pt electrodeposited onto GR, MWCNT, GO, or GONR exhibited poor electrocatalytic activity.

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This study investigated the behavior of thin films of graphene oxide (GO) and chemically converted graphene (CCG) on a glassy carbon surface in the presence of two redox probes (Fe(CN)3−6/Fe(CN)4−6 and O2), employing cyclic voltammetry, electrochemical impedance spectroscopy, and hydrodynamic voltammetry as a simple procedure for characterizing these films. The feasibility of using these electrochemical techniques for this purpose opens up the possibility of applying them to biosensors and electrocatalysts using surface-supported GO and CCG materials. Raman spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy were employed to characterize GO and CCG.