Reaction In Acid Medium Research Articles

Chloride Corrosion Resistant Nitrogen doped Reduced Graphene Oxide/Platinum Electrocatalyst for Hydrogen Evolution Reaction in an Acidic Medium

AbstractImpurities present in the electrolyte often interfere with the electrochemical performance of the electrocatalysts. A robust electrocatalyst can provide corrosion resistance towards the poisoning of contaminants in the electrolyzer. In this present work, N doped graphene and graphene with platinum nanoparticles (NPs) composites (RGO−Pt, U‐NGO−Pt, and A‐NGO−Pt) have been studied against chloride ion poisoning on the performance of hydrogen evolution reaction (HER) in acidic medium. Effect of chloride ion poisoning has been studied by adding Cl‐ ion ranging from 0.16 to 0.96 mM in 0.5 M H2SO4 electrolyte solution. Experimental data revealed that the activated N‐ doped graphene oxide (by KOH at 600 °C) and Pt NPs composite imparts the highest Cl‐ corrosion resistance due to the presence of more pyridinic and pyrrolic groups in the N doped graphene‐Pt composite catalyst. Electrochemical studies showed that A‐NGO−Pt displayed the highest exchange current density (3.20 mA cm−2) and it was nearly 1.3 and 7 times higher than that of RGO−Pt (2.43 mA cm−2) and U‐NGO−Pt (0.46 mA cm−2) respectively. Tafel slope for HER was improved from 35.5 (RGO−Pt) to 32.6 mV dec−1 (A‐NGO−Pt), indicating that the doping of N in the graphene plays an important role in the improvement of the catalytic activity of A‐NGO−Pt catalyst. The impedance spectroscopy, chronoamperometry, chronopotentiometry data in presence of 0.96 mM Cl− ion concentration, LSV curves, and ECSA values before after chronoamperometry for A‐NGO−Pt catalyst confirmed that it was a chloride ion‐resistant, stable and durable electrocatalyst for efficient hydrogen generation by the electrochemical water splitting.

Pulse-reverse electrodeposition of Pt–Co bimetallic catalysts for oxygen reduction reaction in acidic medium

Pt–Co electrodeposited by pulse reverse current on carbon cloth (CC) and glassy carbon (GC) are studied. On both substrates, applying a higher reverse current or a longer reverse-time increases the Pt content due to higher Co dissolution from Pt–Co structures, but does not affect the morphology. Despite similar morphologies and compositions deposited on CC or GC, the electrochemical behaviors of Pt–Co on both substrates are significantly different. Distinct hydrogen under-potential deposition (HUPD) adsorption/desorption peaks are not observed on CC, while well-defined peaks are established on GC. Oxygen reduction reaction (ORR) of Pt–Co on CC is significantly higher than on GC due to its highly porous structure. The ORR on GC changes with the Pt content controlled by varying the reverse pulse during electrodeposition, where Pt–Co with 58 at.% Pt or higher provides a better activity than Pt, with 77 at.% Pt having the highest ORR activity.

Enabling Direct H2O2 Production in Acidic Media through Rational Design of Transition Metal Single Atom Catalyst

Summary The electrochemical oxygen reduction reaction in acidic media offers an attractive route for direct hydrogen peroxide (H2O2) generation and on-site applications. Unfortunately there is still a lack of cost-effective electrocatalysts with high catalytic performance. Here, we theoretically designed and experimentally demonstrated that a cobalt single-atom catalyst (Co SAC) anchored in nitrogen-doped graphene, with optimized adsorption energy of the *OOH intermediate, exhibited a high H2O2 production rate, which even slightly outperformed the state-of-the-art noble-metal-based electrocatalysts. The kinetic current of H2O2 production over Co SAC could reach 1 mA / cm disk 2 at 0.6 V versus reversible hydrogen electrode in 0.1 M HClO4 with H2O2 faraday efficiency > 90%, and these performance measures could be sustained for 10 h without decay. Further kinetic analysis and operando X-ray absorption study combined with density functional theory (DFT) calculation demonstrated that the nitrogen-coordinated single Co atom was the active site and the reaction was rate-limited by the first electron transfer step.

Mesoporous Ni-rich Ni–Pt thin films: Electrodeposition, characterization and performance toward hydrogen evolution reaction in acidic media

Homogeneously mesoporous Ni–Pt thin films have been successfully synthesized by potentiostatic electrodeposition from an aqueous solution. The films are single-phase nanocrystalline Ni–Pt fcc solid solution and their composition can be adjusted with the deposition potential to a Ni content within 60-100 at%. The mesoporosity is constantly present, independent of the composition or microstructure, homogeneously distributed in all dimensions of the films with a pore diameter in the order of 10 nm. Film thickness is uniform and in the range of 200–300 nm. The films show improved performance over an electrodeposited Pt film at hydrogen evolution reaction (HER) and excellent stability in H2SO4 during 200 cycles. For the composition 84 at% Ni and 16 at% Pt, the overpotential required to reach a HER activity of −10 mA/cm2 is as low as −0.09 V vs. RHE. Meanwhile, the mesoporous alloy film with 95 at% Ni exhibits the highest activity with regard to the electrochemical surface area (ECSA).

Rapid synthesis of hollow PtPdCu trimetallic octahedrons at room temperature for oxygen reduction reactions in acid media

Hollow PtPdCu trimetallic octahedrons were prepared under mild conditions, exhibiting enhanced activity toward the oxygen reduction reaction in acid media.

IrCo nanocacti on CoxSy nanocages as a highly efficient and robust electrocatalyst for the oxygen evolution reaction in acidic media.

Developing highly efficient Ir-based electrocatalysts for the oxygen evolution reaction (OER) has been an important agenda in spearheading the water splitting technology. In this study, the synthesis of IrCo nanocacti on CoxSy nanocages (ICS NCs) is demonstrated by utilizing CoO@CoxSy nanoparticles as reactive nanotemplates. In addition to the high catalytic activities with a low overpotential of 281 mV at 10 mA cm-2 and an outstanding mass activity of 1285 mA mgIr-1 at 1.53 V, the ICS NCs endure a prolonged OER test for over 100 h, greatly outperforming other previously reported Ir-based electrocatalysts. This work suggests that the unique hetero-nanostructure of IrCo/CoxSy induces in situ S doping during electrochemical oxidation and the beneficial effect of S doping on the enhanced stability of ICS NCs for the OER.

Surface oxygen-mediated ultrathin PtRuM (Ni, Fe, and Co) nanowires boosting methanol oxidation reaction

The surface-oxygen-modified ultrathin Pt62Ru18Ni20–O/C nanowires catalyst exhibits outstanding mass activity, excellent stability, and CO anti-poisoning for methanol oxidation reaction in acidic medium by DFT and electrochemical experiments.

Ultrathin-shell IrCo hollow nanospheres as highly efficient electrocatalysts towards the oxygen evolution reaction in acidic media.

Improving the utilization of Ir electrocatalysts for the oxygen evolution reaction (OER) to significantly reduce their loading is essential for low-cost hydrogen production in proton exchange membrane water electrolysis. Herein, IrCo hollow nanospheres featuring a novel structure with ultrathin continuous shells which have only eleven atomic layers (2.26 nm) were synthesized by a facile sequential reduction route using NaBH4 as a reducing agent at room temperature. It is revealed that the key intermediate in the formation of hollow nanospheres is amorphous cobalt boride formed between Co2+ and NaHB4 in the first reducing step. The average diameter of the IrCo nanospheres was found to be 73.71 nm with the atomic ratio of 47.1% and 52.9% for Co and Ir, respectively. The IrCo hollow nanospheres exhibit highly efficient OER activity and long-term durability with a low overpotential of 284 mV at 10 mA cm-2 (32.5 μgIr cm-2) and a high mass activity of 8.49 A mg-1 (5.7 times higher than that of commercial IrO2 (1.49 A mg-1) at 1.7 V. The performance is also proved using an overall water splitting device with the overpotential of 318 mV to achieve 10 mA cm-2 as well as a 17 mV shift at 5 mA cm-2 after 14 h. This improvement is critically attributed to the advantages of the hollow structure, ultrathin continuous shells which are oxidized into IrOxin situ and strong lattice strain effects induced by the specific hollow structure and alloying Co into Ir crystal lattices (1.6% against metallic iridium). These characteristics endow the hollow nanospheres with great potential to minimize the Ir loading dramatically for practical applications, compared to other previously reported structures like nanoparticles, nanoneedles and nanowires.

Discovery of crystal structure–stability correlation in iridates for oxygen evolution electrocatalysis in acid

We provide general descriptions regarding the structure–stability correlations of iridium-based complex-oxide catalysts for oxygen evolution reaction in acid media.

Experimental and Theoretical Insights of MoS2/Mo3N2 Nanoribbon‐Electrocatalysts for Efficient Hydrogen Evolution Reaction

AbstractMoS2 is a promising material for electrocatalysis and opens up avenues for the development of non‐precious metal electrocatalysts for hydrogen evolution reaction in acidic media. However, the activity of MoS2 has been severely impeded because of its inferior conductivity. Herein, a nanoribbon‐like MoS2/Mo3N2 hybrid is successfully fabricated via partial sulfidation of Mo3N2 in H2S atmosphere. The synergistic effect between the high intrinsic activity of MoS2 and the desirable conductivity of Mo3N2 contributes to the overpotential at the current density of 10 mA cm−2 (η10) of 196 mV towards hydrogen evolution, distinctively lower than Mo3N2 (467 mV) and MoS2 (293 mV). The theoretical simulation discloses that the Gibbs free‐energy for the adsorption of atomic hydrogen (|ΔGH*|) for MoS2/Mo3N2 is less than that of others, and thus facilitating the hydrogen evolution.

Halide adsorption effect on methanol electro-oxidation reaction studied by dynamic instabilities

The effect of halide anion adsorption on methanol electro-oxidation reaction in acid media was studied by means of thermal effects on both cyclic voltammograms (CV) and oscillations in galvanostatic time series (GTS). While increasing the chloride concentration we observed a monotonically current decrease followed by an increase of apparent activation energy (Ea) in CV, GTS increases the maximum potential (Emax) and decreases both the oscillation frequency (w) and Ea. Poisoning/Freeing rates (dE/dt) increase for a very small Cl− amount but decreases for higher concentrations. Changing Cl− by Br−, albeit observing similar behaviors for currents on CV and w, Emax and Ea changes suggest that Br− probably plays a dual role, i.e. poisoning the surface by its adsorption but also interacting with adsorbed methanol residues. Finally, increasing the pH to 5.6 in a nonadsorbing electrolyte (HClO4/NaF) several oscillations patterns were mapped with a lesser Cl− influence on both CV and GTS.

Ag-Cd-B-P ternary alloy with efficient electrocatalytic activity towards hydrogen evolution reaction (HER)

Recently, a stable and effective Pt-free electrocatalyst is hugely required for hydrogen generation through water splitting. In this article, we present an easy synthesis of very small particle sized electrocatalysts Ag-Cd-B-P and Cd-Ag-B-P with good catalytic activity and stability for electrochemical hydrogen evolution reaction in acidic medium. Ag-Cd-B-P catalyst exihibits better performance than Cd-Ag-B-P with lower onset potential of - 0.25 V, higher electrochemical surface area of 0.50 cm2, excellent current density of 1.18 A/cm2 at – 1.29 V, low tafel slop of 118 mV/dec and small overpotential of 50 mV to achieve 10 mA/cm2 current density. The reported Ag-Cd-B-P electrocatalyst shows good storage stability of 2 months in normal condition with only ∼2 % change in onset potential and current density.

Facile synthesis of SrIrO3 by mechanical activation assisted solid-state reaction for efficient oxygen evolution reaction in acidic media

Oxygen evolution reaction (OER) is an anodic reaction for copper electrowinning that occurs during the hydrometallurgical manufacturing process of copper, and the development of a highly active catalyst for the OER in an acidic electrolyte is of vital importance in terms of energy saving. Herein, we report a facile method to synthesize the SrIrO3 catalyst by solid-state reaction method assisted by mechanical activation. The results demonstrated that mechanical activation is critical to the successful fabrication of the SrIrO3 catalyst. XRD and TEM results confirmed the formation of SrIrO3 without other impurities, and XPS results revealed that some of the Ir species, including Ir4+, existed in +3 valence states. The catalyst shows both high catalytic activity for OER and stability in a sulfuric acid solution, with a Tafel slope of 48 mV dec−1 and almost no current decay after 1000 voltammetry cycles. This investigation is of fundamental and practical importance for synthesizing highly efficient SrIrO3 OER electro-catalysts to be potentially applied in copper electrowinning.

Mesoporous graphitic carbon nitride synthesized using biotemplate as a high-performance electrode material for supercapacitor and electrocatalyst for hydrogen evolution reaction in acidic medium

Abstract Mesoporous graphitic carbon nitride (MGCN) is extensively studied as a catalyst for various processes, such as photocatalysis, CO2 reduction, etc. Recently, it has been used as an electroactive material for supercapacitor. This article reports the improved capacitance properties and enhanced electrocatalytic activity of MGCN towards hydrogen evolution reaction (HER). MGCN is synthesized by using environmentally benign, biotemplate, namely, carboxymethyl cellulose. X-ray diffraction and electron microscopic studies confirm the formation of the stacked layer structure. X-ray photoelectron spectroscopic, elemental analysis, thermogravimetric analysis, and nitrogen sorption studies reveal that C/N ratio and surface area of MGCN depend on the precursor to the template ratio. A highest specific capacitance of 286 F g−1 is obtained at a current density of 0.75 A g−1 for MGCN synthesized using 0.3 g of carboxymethyl cellulose (MGCN-0.3), which is higher than that of MGCN synthesized using 0.1 (MGCN-0.1), and 0.5 g (MGCN-0.5) of carboxymethyl cellulose. Supercapacitor devices fabricated in symmetrical configuration using MGCN-0.3 outperforms various nitrogen doped carbonaceous materials. On the other hand, overpotential of 272 mV s−1 at a current density of 10 mA cm−2 and a Tafel slope of 101 mV dec−1 obtained for MGCN-0.5 towards HER is better than that of several composites of graphitic carbon nitride reported in the literature.

Production of fatty acid methyl esters and bioactive compounds from citrus wax

Citrus wax is a waste generated during the purification process of the citrus essential oil. A lot of citrus wax wastes are globally produced, despite this, its composition and properties are not well known. Here we present comprehensive results proving the chemical composition and the physical properties of citrus wax. Additionally, our study provides the basis for obtaining value-added products from citrus wax wastes. The qualitative/quantitative analysis revealed the presence of different compounds, which range from flavonoids, saponins, carbohydrates, unsaturated compounds, phenolic hydroxyls, and long-chain fatty acid esters. Given that citrus wax is a source of many bioactive compounds, they were preferably extracted with ethanol. The ethanolic extracts demonstrated the presence in citrus wax of different bioactives, such as 5–5′-dehydrodiferulic acid, 3,7-dimethylquercetin, 5,6-dihydroxy-7,8,3′,4′-tetramethoxyflavone, tangeretin, and limonene. After the extraction of bioactives from citrus wax, a washed waxy material with high content of long-chain fatty acid esters was obtained. It was shown that this washed wax can be used for the production of biodiesel. The transesterification reactions in acid media was the preferred process because higher content of fatty acid methyl esters (such as hexadecanoic acid methyl ester and 9,12-octadecadienoic acid (Z,Z)-, methyl ester) were obtained. Currently, citrus wax does not have any industrial application, here we shown that under the concept of waste biorefinery, the citrus wax wastes are useful sources for producing value-added products such as bioactive compounds and biodiesel.

Single Fe atoms anchored by short-range ordered nanographene boost oxygen reduction reaction in acidic media

The development of efficient and stable single-atom electrocatalysts with earth-abundant metals have emerged as a promising alternative to the costly Pt-based nanomaterials for oxygen reduction reaction (ORR). Herein, we synthesize a highly efficient electrocatalyst with single Fe atoms anchored by N-doped short-range ordered carbon loading on 2 D reduced graphene oxide (RGO). Unlike the highly graphitized carbon materials in previous ORR catalysts, in which the diffusion of oxygen molecules (∼3.46 Å) are blocked by long carbon chains and small interlayer spacing (∼3.4 Å), it is found that the Fe/N-doped nanographene possesses large interlayer spacing (>4 Å) and short carbon fragments in one layer. The unique nanographene structure in nanoscale can facilitate the transport of oxygen molecules to the active sites of atomically dispersed FeN4 and FeN5. In acidic media for ORR, as-prepared Fe1-N-NG/RGO catalyst exhibited half-wave potential (E1/2) of 0.84 V versus the reversible hydrogen electrode, and the loss of E1/2 is less than 5 mV during 15,000 potential cycles.

Reduced graphene oxide-supported CoP nanocrystals confined in porous nitrogen-doped carbon nanowire for highly enhanced lithium/sodium storage and hydrogen evolution reaction

Rational synthesis of a hierarchical porous architecture with highly active and consecutive conductive network is very critical to achieve the high-performance of nanomaterials in electrochemical energy conversion and storage. We propose here a hierarchical micro-/nanostructured hybrids constructed by the dual carbon shell nanowire host containing CoP nanocrystals of several nanometers, which generates Co-based metal-organic framework on graphene oxide nanosheets in situ and followed a direct phosphorization (CoP@NC/rGO). The dual carbon shell, consisting of Co-based metal-organic framework derived porous doped carbon (NC) and reduced graphene oxide (rGO), can not only impedes CoP nanocrystals from coalescing, and renders highly exposed the electrochemically accessible active sites, but also provides the multidimensional pathways for rapid electron and ion transportation. More importantly, the covered dual carbon shell on CoP nanocrystals plays a role as a protective layer to impede the nanocrystals’ corrosion. By virtue of compositional and structural advantages, the micro-/nanostructured CoP@NC/rGO hybrids manifest outstanding energy storage properties when evaluated as anodes for lithium/sodium ion batteries. Remarkably, it also reveals highly efficient electrocatalytic performance for hydrogen evolution reaction in acid media with low Tafel slope, overpotential and robust durability.

Highly efficient Ni0.5Fe0.5Se2/MWCNT electrocatatalyst for hydrogen evolution reaction in acid media

In the present energy scenario of the world, hydrogen with high energy content seems to be a better green alternative to depleting fossil fuels. Here we describe an innovative and efficient iron nickel diselenide (Ni0.5Fe0.5Se2) as a potential electrocatalyst for hydrogen evolution reaction in acid media. Ni0.5Fe0.5Se2 has been fabricated by means of one-step hydrothermal process supported by multi walled carbon nanotubes (MWCNTs). Ni0.5Fe0.5Se2/MWCNTs electrocatalyst has been prepared from cost-effective and highly available earth-abundant elements. The crystalline structure, morphology and elemental composition of Ni0.5Fe0.5Se2/MWCNTs with different weight percentage (1, 3, 5, 7%) of MWCNTs in the composite. The electrocatalysts has been successfully evaluated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), field emission scanning electron microscopy (FE-SEM). Cyclic voltammetry (CV), Tafel and electrochemical impedance analysis have been utilized to investigate. Among the investigated weight percentages, the electrocatalyst with 3 wt% of MWCNT exhibited high hydrogen evolution activity with a current density of 10 mA/cm2 at an overpotential 200 mV with a Tafel slope of 71 mVdec−1. The synergistic efforts between Ni0.5Fe0.5Se2 and MWCNTs in the promotion of hydrogen evolution activity is ascribed to active sites, low electron transfer resistance and superior electrochemical kinetics of molecular hydrogen (H2) production.

Determination of trace amounts of selenium in natural spring waters and tea samples by catalytic kinetic spectrophotometry

In this work, a new kinetic method is described for the determination of trace Se(IV) in natural spring waters and commercial tea samples. The method is based on the activation of Se(IV) onto the indicator reaction in acidic medium. The reaction was monitored using a fixed time approach of 20 min at 680 nm. The variables affecting the reaction rate were evaluated and optimized. The method allows the determination of Se(IV) in the range of 0.0125-1.0 mg L-1 with a detection limit of 3.6 µg L-1. The precision was in range of 0.63-3.15% (as RSD %) with a higher recovery than 98.6%. The method has been found to be selective against matrix effect. The method was applied to the speciation analysis of inorganic Se species present in the selected samples. The method was statistically validated by analysis of two certified samples and comparing the obtained results to those of HG-AAS analysis. Also, the total Se levels of the samples were determined by using both methods after conversion of Se(VI) into Se(IV) in ultrasonic bath in acidic medium for 30 min at 85-90 °C. The results were in good agreement with those of HG-AAS. The Se(VI) level of the samples was calculated from the difference between amounts of total Se and Se(IV).

Active‐Site Imprinting: Preparation of Fe–N–C Catalysts from Zinc Ion–Templated Ionothermal Nitrogen‐Doped Carbons

AbstractAtomically dispersed Fe–N–C catalysts are considered the most promising precious‐metal‐free alternative to state‐of‐the‐art Pt‐based oxygen reduction electrocatalysts for proton‐exchange membrane fuel cells. The exceptional progress in the field of research in the last ≈30 years is currently limited by the moderate active site density that can be obtained. Behind this stands the dilemma of metastability of the desired FeN4 sites at the high temperatures that are believed to be a requirement for their formation. It is herein shown that Zn2+ ions can be utilized in the novel concept of active‐site imprinting based on a pyrolytic template ion reaction throughout the formation of nitrogen‐doped carbons. As obtained atomically dispersed Zn–N–Cs comprising ZnN4 sites as well as metal‐free N4 sites can be utilized for the coordination of Fe2+ and Fe3+ ions to form atomically dispersed Fe–N–C with Fe loadings as high as 3.12 wt%. The Fe–N–Cs are active electocatalysts for the oxygen reduction reaction in acidic media with an onset potential of E0 = 0.85 V versus RHE in 0.1 m HClO4. Identical location atomic resolution transmission electron microscopy imaging, as well as in situ electrochemical flow cell coupled to inductively coupled plasma mass spectrometry measurements, is employed to directly prove the concept of the active‐site imprinting approach.