Reaction In Acid Medium Research Articles

A novel cobalt tungstate and reduced graphene oxide composite for hydrogen evolution reaction in acid medium

Due to the serious energy shortage and environmental pollution caused by fossil fuel, developing a renewable energy source is crucial. In this work, non-precious cobalt tungstate nanoparticles embedded reduced graphene oxide (CoWO4@rGO) based electrocatalyst is developed for hydrogen evolution reaction (HER) in an acidic medium. The fabricated catalyst shows a superior HER activity with an overpotential of −0.57 V versus reversible hydrogen electrode (RHE) at 10 mA/cm2 and a Tafel slope of 142 mV/dec. The work established a simple strategy to develop a stable and low-cost catalyst for HER, which attain great attention for the development of a clean energy landscape.

Influence of Electrochemical Pretreatment Conditions of PtCu/C Alloy Electrocatalyst on Its Activity.

A carbon supported PtCux/C catalyst, which demonstrates high activity in the oxygen electroreduction and methanol electrooxidation reactions in acidic media, has been obtained using a method of chemical reduction of Pt (IV) and Cu (2+) in the liquid phase. It has been found that the potential range of the preliminary voltammetric activation of the PtCux/C catalyst has a significant effect on the de-alloyed material activity in the oxygen electroreduction reaction (ORR). High-resolution transmission electron microscopy (HRTEM) demonstrates that there are differences in the structures of the as-prepared material and the materials activated in different potential ranges. In this case, there is practically no difference in the composition of the PtCux-y/C materials obtained after activation in different conditions. The main reason for the established effect, apparently, is the reorganized features of the bimetallic nanoparticles’ surface structure, which depend on the value of the limiting anodic potential in the activation process. The effect of the activation conditions on the catalyst’s activity in the methanol electrooxidation reaction is less pronounced.

Biomass-derived precious metal-free porous carbon: Ca-N,P-doped carbon materials and its electrocatalytic properties

The search for non-noble metal catalysts drive from biomass materials for oxygen reduction reactions (ORR) is highly desirable but challenging. Here, we have designed and synthesized three-dimensional hierarchical porous Ca-modified nitrogen and phosphorus co-doped carbon materials (Ca@NP6C4) derived from biomass hydrogel. Notably, the resulting Ca@NP6C4 material has high content of nitrogen (29.71 wt%)，and relatively high content percentage of pyridinic and graphitic nitrogen. As an efficient non-noble metal electrocatalyst, Ca@NP6C4 exhibits a high onset potential (0.94 V vs RHE) and a four-electron pathway for oxygen reduction reaction as well as good durability and outstanding methanol poisoning tolerance. Besides, it also performs as a good support for Pt particles (NPs). Pt/Ca@NP6C4 catalyst displayed remarkable catalytic performance and high stability for methanol electrooxidation reaction in acid medium. This work provides a feasible approach to develop cost-effective and highly efficient non-precious metal electrochemical catalysts for oxygen reduction.

Electrocatalysis for the Oxygen Evolution Reaction in Acidic Media: Progress and Challenges

The oxygen evolution reaction (OER) is the efficiency-determining half-reaction process of high-demand, electricity-driven water splitting due to its sluggish four-electron transfer reaction. Tremendous effects on developing OER catalysts with high activity and strong acid-tolerance at high oxidation potentials have been made for proton-conducting polymer electrolyte membrane water electrolysis (PEMWE), which is one of the most promising future hydrogen-fuel-generating technologies. This review presents recent progress in understanding OER mechanisms in PEMWE, including the adsorbate evolution mechanism (AEM) and the lattice-oxygen-mediated mechanism (LOM). We further summarize the latest strategies to improve catalytic performance, such as surface/interface modification, catalytic site coordination construction, and electronic structure regulation of catalytic centers. Finally, challenges and prospective solutions for improving OER performance are proposed.

IrRuOx/TiO2 a stable electrocatalyst for the oxygen evolution reaction in acidic media

Proton Exchange Membrane Electrolysis of Water (PEMWE) stands out as a scalable, CO2-free process to produce H2 for energy delivery and industrial applications. Due to the limited Ir and Ru worldwide availability, one of the main challenges for the GW-scale PEMWE implementation is the loading reduction of these metals in the anodic catalytic layer. Here, Ir–Ru loading (5 wt%Ir-40 wt%Ru) was deposited through their impregnation over TiO2, followed by a thermal-oxidative treatment, obtaining IrRuOx/TiO2 catalyst. SEM-EDS and HR-TEM confirmed the homogeneous dispersion of IrRuOx on TiO2. The supported catalyst showed a 1.4-fold higher mass activity (85 mA/mg Ir–Ru) for the oxygen evolution reaction (OER) than a mechanical mixture of IrO2–RuO2 1:3 (54 mA/mgIr+Ru) in H2SO4 0.5 M, at 1.52 V/RHE. Furthermore, the supported catalyst retains 90% of its catalytic activity after 100 reaction cycles suggesting the RuO2 intermediate species stabilization by IrOx, which can avoid its irreversibly transform into hydrous RuOx.

Low-Cost Pb-Co-Sn film for the Oxygen Evolution Reaction in Acid Media

The oxygen evolution reaction (OER) plays an important role in several industrial processes. However, the high overpotential that the OER requires to take place, has resulted in high costs associated with precious metals used in anodes that catalyze this reaction. Substitute elements, among them Co, have been investigated in order to decrease their price, herein, highlight Pb-Co electrodes that achieved an important decrease in the overpotential needed for the OER. Even though the electrocatalyst ability showed by the Pb-Co anode was considerably high, the current densities achieved were too low to compete with commercial anodes. Therefore, the efficiency to produce O2 should be increased. The aim of this work was to develop a Pb-Co-Sn film, through anodic electrodeposition, that enables an efficient production of O2 coupled with stability, low-cost and low overpotential. In order to know the morphological, microstructural and chemical composition, a full characterization of the developed film was carried out. The obtained Pb-Co-Sn film showed higher electrochemical performance than conventional Pb-Ca-Sn anodes, with an overpotential of ∼0.27 V vs NHE at 500 Am−2, 68% lower than a conventional Pb-Ca-Sn anode.

High‐dispersion Co‐Fe‐NC electrocatalyst based on leaf‐shaped zeolite imidazole framework for oxygen–reduction reaction in acidic medium

Platinum-free electrocatalysts for oxygen–reduction reactions in acidic medium are challenging as the cathode of PEMFC. Here, we synthesized core-shell-type leaf-shaped CoFe-NC (L-CoFe-NC) catalysts using 2D ZIFs as cores and 3D ZIFs as shells. The amounts of Co and Fe were carefully controlled to obtain highly dispersed CoFe-doped carbon. This strategy made it easy to tune the catalyst while maintaining the advantages of the 2D structures. The prepared L-CoFe-NC showed a half-wave potential (E1/2) of 0.77 V and an onset potential (Eonset) of 0.88 V in 0.5 M H2SO4. In addition, the results confirmed high durability even after 10 000 tests while retaining excellent performance. This outstanding stability was achieved owing to the high dispersion of Co and Fe in the 2D carbon frame. Furthermore, PEMFC was evaluated using an MEA containing L-CoFe-NC catalysts as a cathode.

Substituents and the induced partial charge effects on cobalt porphyrins catalytic oxygen reduction reactions in acidic medium

Charge states at the catalytic interface can intensely alter the charge transfer mechanism and thus the oxygen reduction performance. Two symmetric cobalt porphyrins with electron deficient 2,1,3-benzothiadiazole (BTD) and electron-donating propeller-like triphenylamine (TPA) derivatives have been designed firstly, to rationally generate intramolecular partial charges, and secondly, to utilize the more exposed molecular orbitals on TPA for enhancing the charge transfer kinetics. The catalytic performance of the two electrocatalysts was examined for oxygen reduction reactions (ORR) in acidic electrolyte. It was found that BCP1/C with two BTD groups showed greater reduction potential but less limiting current density as compared to BCP2/C bearing BTD-TPA units. The reduced potential of BCP2/C was proposed to the introduction of the electron-donating ability of TPA, which may decrease the adsorption affinity of oxygen to the cobalt center. Both dipole-induced partial charge effect and the more exposed cation orbitals of the 3D structural TPA were proposed to contribute to the increased response current of BCP2/C. In addition, BCP2/C attained more than 80% of H2O2 generation in acidic solution, which may also relate to the structural effect. These findings may provide new insight into the structural design of organic electrocatalysts and deep understanding on the interfacial charge transfer mechanism for ORR.

The Effect of Tuning the Coordination Sphere of Iron Complexes for the Oxygen Reduction Reaction in Acidic Media

As a type of important non-precious catalyst for the oxygen reduction reaction (ORR), the regulating role of a metal centre in metal-macrocycles and other complexes for activity has been extensively studied. However, a common guideline to explain the effect of peripheral coordinated-ligands has not been reached. Herein, a series of organic iron complexes (denoted as FeL, L = TAA, Pc, TPP, Corrole, Tim and Salen) were synthesized as ORR catalysts and an explicit relationship of structure-activity was constructed. The kinetic current density for these compounds was identified to follow the order of FeTAA > FePc > FeTPP > FeCorrole > FeTim > FeSalen. An electron-transfer number close to 4 was derived for all these complexes except for FeTim and FeSalen, implying a near complete reduction of oxygen to water. X-ray absorption near edge structure spectroscopy (XANES) and Mössbauer spectroscopy were used to probe the nature of the distinct activities by investigating the iron-centre electron structures. Density function theory (DFT) calculations were carried out to study the charge redistribution across the iron complexes. Novel activity descriptors including the charge and spin densities on the Fe site were proposed and validated by available experimental data, presenting a strategy to design highly-active nonprecious metal complex catalysts with specific supporting ligands.

Iridium Oxide Modified with Silver Single Atom for Boosting Oxygen Evolution Reaction in Acidic Media

Electrocatalytic oxygen evolution in acidic media is crucial for promoting water splitting. Herein, we report an Ag1/IrOx single atom catalyst (SAC) with Ag single atoms embedded in an IrO2 matrix ...

Copper and iron mediated growth of surfactant‐free PtCu and PtFe advanced electrocatalysts for water oxidation and oxygen reduction

AbstractPt‐based alloy nanoparticles are critical electrochemical catalysts for the water oxidation and oxygen reduction reactions. But the surfactants adsorbed on the nanoparticles’ surfaces are hard to remove off, blocking the catalytic active sites and decrease the catalysis activity of the alloy catalysts. Herein, we engineered surfactant‐free PtCu alloy polyhedral nanospheres with foam‐like surfaces in pure water at 40°C directly. Metal precursors were reduced by ascorbic acid. The sizes of polyhedral nanospheres were formed by assembling of tiny PtCu alloy nanoparticles in the sizes of 4.2 ± 0.70 nm, resulting the larger nanospheres in the sizes of 124 ± 30 nm. Underpotential deposition of copper atoms occurred, which catalyzed reductions of Pt precursor and depositions of Pt atoms, high yields of Pt component in PtCu alloy nanospheres and fast reaction rate for reductions of Pt precursors were achieved. Common transition metal, Fe, Co, Ni was also investigated. Only Fe atoms were alloyed with Pt crystals, but the contents of Fe were lower than those of Cu in PtCu alloy. Due to the alloyed structures and special surface structures, PtFe and PtCu exhibited 12.8% and 87% higher current densities toward water oxidation reaction and oxygen reduction reactions in acidic medium than those of commercial Pt black, respectively. This work provides us a new way to get surfactant‐free PtM (M = Cu, Fe, etc) alloy nanoparticles which were produced in water. It is significant to achieve the advanced electrocatalysts with clean surfaces and high catalytic activities.

Hydrogen Evolution and Oxygen Reduction Reactions in Acidic Media Catalyzed by Pd4 S Decorated N/S Doped Carbon Derived from Pd Coordination Polymer.

The template-free synthesis and the characterization of an active electrocatalyst are performed for both the hydrogen evolution and oxygen reduction reactions in acidic media. In this work, the unique chelation mode of benzene-1,4-dithiocarboxamide (BDCA) is first used to synthesize a novel palladium-BDCA coordination polymer (PdBDCA) as a precursor of palladium sulfide nanoparticles-decorated nitrogen and sulfur doped carbon (Pd4 S-SNC). The newly synthesized PdBDCA and Pd4 S-SNC nanoparticles are characterized using chemical, electrochemical, and surface analysis methods. Notably, the nanoparticles obtained at 700°C exhibit the remarkable catalytic property for the hydrogen evolution reaction in 0.5 m H2 SO4 , showing the overpotential of 32mV (vs reversible hydrogen electrode (RHE)) and Tafel slope of 52mV dec-1 , which are comparable to that of Pt/C. The catalyst also shows a high oxygen reduction activity, offering the half-wave and onset potentials of 0.92 and 0.77V (vs RHE) in 0.5 m H2 SO4 , with improved methanol tolerance and long-term stability compared with Pt/C. The present study gives a way for the design of excellent electrocatalyst for the energy conversion devices in the corrosive acidic environment.

Praseodymium iridium oxide as a competitive electrocatalyst for oxygen evolution reaction in acid media

Amorphous iridium oxides (IrOx) are highly active for oxygen evolution reaction (OER) in acid media; however, it is generally unstable compared with commercial IrO2. Recently, many non-noble metal-iridium mixed oxides are prepared for catalyzing OER efficiently. Herein, we report a cubic fluorite-type praseodymium iridium oxide with the surface of IrOx (IrOx/Pr3IrO7) that shows the improved activity and stability in 0.1 mol L−1 HClO4 solution, characterized by an overpotential of 305 mV at the benchmark of 10 mA cm−2 and a small Tafel slope of 37 mV dec−1, indicating a fast reaction kinetics and a competitive activity compared with the benchmark IrO2 and most reported electrocatalysts. The initial potential increases by less than 0.07 V after continuous OER testing over 60,000 s. In contrast, IrO2 becomes nearly inactive for the OER within 20,000 s. Density functional theory calculations uncover that the optimal energy level path follows lattice oxygen mechanism (LOM). This work enlarges the family of the IrOx-type OER electrocatalyst in acid media.

Three-Dimensional Needle Branch-like PANI/CoNiP Hybrid Electrocatalysts for Hydrogen Evolution Reaction in Acid Media

In this work, a kind of three-dimensional (3D) needle branch-like array nanostructured PANI/CoNiP hybrid electrode self-supported on nickle foam (NF) is explored. This 3D needle branch-like array n...

FeNi-functionalized 3D N, P doped graphene foam as a noble metal-free bifunctional electrocatalyst for direct methanol fuel cells

Designing high-performance bifunctional electrocatalysts for oxygen reduction (ORR) and methanol oxidation (MOR) reaction is essential for the wide application of direct methanol fuel cells. Here, we have prepared a novel three-dimensional (3D) FeNi-functionalized N, P doped graphene foam (FeNi@NP-GF) by a simple and cost-effective one-step pyrolysis method, as excellent bifunctional electrocatalyst for direct methanol fuel cells. Compared with metal-free and transition metal single-doped graphene foam catalysts (NP-GF, Fe@NP-GF and Ni@NP-GF), the resulting FeNi@NP-GF catalyst showed more positive half-wave potential and higher limiting current density in ORR reaction. Furthermore, it manifests a four-electron transfer process and strong methanol crossover resistance in the alkaline medium. The above results ascribed to the synergistic effect of Fe/Ni-Nx species formed with Fe/Ni and N species and multiple active sites in the 3D porous graphene material. Moreover, FeNi@NP-GF acted as good support for Pt nanoparticles (NPs). Pt/FeNi@NP-GF catalyst displayed remarkable catalytic performance and high stability for methanol electrooxidation reaction in acid medium.

Synthesis of metal and non-metal doping hematite nanoparticles for adsorption and photocatalytic degradation of acid red 14 in aqueous solutions

ABSTRACT Adsorption and photocatalytic decolourisation of AR14 in aqueous solution was investigated using α-Fe2O3, α-Fe2O3/S and α-Fe2O3/CdS in dark and under UV irradiation, respectively. The synthesis of alpha iron oxide nanoparticles and combining heteroatoms in its matrix were performed by a simple co-precipitation method. Samples were characterised by XRD, Raman and pHPZC. The dye adsorption on the catalysts’ surfaces showed a strong dependence on the pH, and the adsorption played the main role in the photocatalytic reaction in acidic medium. The pseudo first order kinetic model was found to be the best fit for the adsorption of AR14 by the three catalysts (R2 > 0.99) and is in good agreement with a chemisorption mechanism. The plot of intra-particle diffusion model showed a three-stage adsorption process which suggests that more than one process affects the AR14 adsorption. α-Fe2O3/S and α-Fe2O3/CdS nanoparticles had significant enhancement on the decolourisation of AR14 compared to the bulk material. A rate removal of 78%, 94% and 98% of the AR14 was recorded at pH = 3 under UV irradiation for α-Fe2O3, α-Fe2O3/S and α-Fe2O3/CdS respectively. The decolourisation was strongly enhanced in the presence of H2O2 leading to Fenton-like process. Added H2O2 competes with AR14 for the powder surface sites and reduces its adsorption on the catalysts’ surfaces. The addition of propanol-2 as a radical scavenger confirms that •OH radicals are the main species responsible for the decolourisation of AR14 inα-Fe2O3/H2O2 system. Fenton-like process provides more selective oxidation for AR14 that have a higher affinity for the iron oxide surface and also for the modified iron oxide surface.

Rh2P Activity at a Fraction of the Cost? Co2–xRhxP Nanoparticles as Electrocatalysts for the Hydrogen Evolution Reaction in Acidic Media

The composition-dependent hydrogen evolution reaction (HER) activity of Co2–xRhxP nanoparticles in acid is reported. The motivation for the current study stems from (1) prior work demonstrating tha...

Hetero Atom Doped Graphene Nanoarchitectonics as Electrocatalysts Towards the Oxygen Reduction and Evolution Reactions in Acidic Medium

Oxygen electrocatalysis plays a vital role in sustainable energy solutions concerning the storage and conversion using electrical energy into chemical energy and vice versa. The important processes in oxygen electrocatalysis includes oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remain clean affordable efficient and economically feasible solutions. Carbon based metal-free materials owing to their abundance, electrical conductivity, porosity, structural modification at the molecular levels and exceptional stability under harsh conditions are emerging as advanced electrodes toward the design of high-performance oxygen electrocatalysts. This review provides a critical overview of this rapidly developing field including the design of efficient hetero atom doped graphene-based metal-free catalysts, defect engineering and co-doping with special emphasis on the electrochemical activity in acidic media. The latest trends in the design of hetero atom doped graphene nanoarchitectonics for ORR and OER along with important electrochemical parameters in the field were also outlined. Furthermore, the design of efficient and robust bi-functional hetero atom doped graphenes elucidating structure-property relationship toward multifunctional OER/ORR behaviour was highlighted. The key challenges and future opportunities in this exciting field are profoundly discussed.

Metal- and Nonmetal-Incorporated Vitamin B <sub>12</sub> on Graphene as a Bioderived Electrocatalyst for High-Performance Oxygen Reduction Reaction in Acidic Media

Metal- and Nonmetal-Incorporated Vitamin B <sub>12</sub> on Graphene as a Bioderived Electrocatalyst for High-Performance Oxygen Reduction Reaction in Acidic Media

Multimetallic nanostructures for electrocatalytic oxygen evolution reaction in acidic media

In this review, the authors highlighted the recent progress on the noble metal-based multimetallic electrocatalysts toward the oxygen evolution reaction under acidic condition.