Hollow Ni Mo-based nitride heterojunction with super-hydrophilic/aerophobic surface for efficient urea-assisted hydrogen production

Hydrogen evolution reaction(HER)and urea oxidation reaction(UOR)are key reactions of the watercycling associated catalytic process/device.The design of catalysts with a super-hydrophilic/aerophobic structure and optimized electron distribution holds great promise.Here,we have designed a threedimensional(3D)hollow Ni/NiMoN hierarchical structure with arrayed-sheet surface based on a onepot hydrothermal route for efficient urea-assisted HER based on a simple hydrothermal process.The Ni/NiMoN catalyst exhibits super-hydrophilic/aerophobic properties with a small droplet contact angle of 6.07°and an underwater bubble contact angle of 155.7°,thus facilitating an escape of bubbles from the electrodes.Density functional theory calculations and X-ray photoelectron spectroscopy results indicate the optimized electronic structure at the interface of Ni and NiMoN,which can promote the adsorption/desorption of reactants and intermediates.The virtues combining with a large specific surface area endow Ni/NiMoN with efficient catalytic activity of low potentials of 25 mV for HER and 1.33 V for UOR at10 mA cm^(-2).The coupled HER and UOR system demonstrates a low cell voltage of 1.42 V at 10 mA cm^(-2),which is approximately 209 mV lower than water electrolysis.

Detection of Oxidants Such as Hydroxyl Radicals and Chlorine Electrogenerated on a BDD Electrode by Simple Methods

The aim of this work is to detect electrogenerated hydroxyl radicals and chlorine by simple and less expensive methods. Preparative electrolyses of perchloric acid (HClO4) and sodium chloride (NaCl) were performed on a boron-doped diamond (BDD) electrode. The hydroxyl radicals were quantified indirectly by assaying the samples from the HClO4 (0.1 M) electrolysis with a 10−4 M potassium permanganate solution. The investigations showed that the amount of hydroxyl radicals depends on the concentration of HClO4 and the current density. As for chlorine, a qualitative determination was carried out. A mixture of the electrolyte solution of HClO4 (0.1 M) + NaI (0.2 M) + 2 mL of hexane, taken in this order, leads to a purplish-pink coloration attesting to the presence of Cl2. The same test was carried out with NaBr and NaI giving pale and very pale pink colourations, respectively, showing that the intensity of the colouration depends on the strength of the oxidant present. In addition, oxidants were detected during the electrooxidation of metronidazole (MNZ). The results showed the participation of electrogenerated hydroxyl radicals. The generation of chlorine has also been proven. Furthermore, the degradation leads to a chemical oxygen demand (COD) removal rate of 83.48% and the process is diffusion-controlled.

Tailoring the selective adsorption sites of NiMoO by Ni particles for biomass upgrading assisted hydrogen production

5-Hydroxymethylfurfural electrooxidation reaction(HMFOR)is a promising route to produce valueadded chemicals from biomass.Since it involves HMF adsorption and C-H/O-H cleavage,understanding the adsorption behavior and catalytic process of organic molecules on catalysts is important.Herein,the selective adsorption sites of NiMoO are tuned by Ni particles for HMFOR-assisted H2production.Experimental and theoretical calculation results indicate that the synergistic interaction between Ni and NiMoO optimizes the adsorption/desorption of HMF/intermediates/2,5-furandicarboxylic acid(FDCA)and promotes the C-H/O-H bond cleavage,thereby improving the HMFOR kinetics(kNiMoO-Ni/kNiMoO=1.97)and FDCA selectivity(99.3%).When coupled as a two-electrode system,it can drive efficient HMF conversion(FDCA yield:98.5%)and H2production(Faradaic efficiency:99.1%)at 1.45 V.This work thus offers a strategy to tune the adsorption sites of catalyst for efficient HMFOR-assisted H2production.

Pt-Te alloy nanowires towards formic acid electrooxidation reaction

The high-performance anodic electrocatalysts is pivotal for realizing the commercial application of the direct formic acid fuel cells.In this work,a simple polyethyleneimine-assisted galvanic replacement reaction is applied to synthesize the high-quality PtTe alloy nanowires(PtTe NW)by using Te NW as an efficient sacrificial template.The existence of Te atoms separates the continuous Pt atoms,triggering a direct reaction pathway of formic acid electrooxidation reaction(FAEOR)at PtTe NW.The one-dimensional architecture and highly active sites have enabled PtTe NW to reveal outstanding electrocatalytic activity towards FAEOR with the mass/specific activities of 1091.25 mA mg^(-1)/45.34 A m^(-2)at 0.643 V potential,which are 44.72/23.16 and 20.26/11.75 times bigger than those of the commercial Pt and Pd nanoparticles,respectively.Density functional theory calculations reveal that Te atoms optimize the electronic structure of Pt atoms,which decreases the adsorption capacity of CO intermediate and simultaneously improves the durability of PtTe NW towards FAEOR.This work provides the valuable insights into the synthesis and design of efficient Pt-based alloy FAEOR electrocatalysts.

Electrochemically and Ultrasonically-Enhanced Coagulation for Algae Removal

At the global level, the augmenting presence of harmful algae blooms constitutes important dares to water treatment plants (WTPs). In WTPs, coagulation remains the primary process of the applied procedure to treat algae-contaminated water. Such a chemical process influences the following techniques;thus, regulating coagulation parameters to eliminate algae at the maximum degree without provoking cell deterioration is more than crucial. This work aims to review coagulation-founded methods for algae elimination. First, investigations concentrating on algae elimination using the chemical process are discussed. The introduction presents the widespread algae encountered in the water treatment field. Then, habitually utilized experimental techniques and emerging methods in coagulation investigations are summarized with typical findings. Next, the newest expansions in improved algae elimination, launched by electrochemically and ultrasonically-enhanced coagulation, are discussed. Workable thoughts for applying coagulation to eliminate algae in WTPs are also debated. The paper finishes by defining restrictions and dares related to the present literature and suggesting trends for subsequent studies. The charge neutralization mechanism efficiently removes solubilized microcystins (MCs), and enhanced coagulation configuration is also found to be more efficient for their removal. However, considerations should be taken to avert that the acid introduction has no unwanted effect in killing algae treatment to avoid the solubilized MCs level elevation. If such techniques are well-optimized and controlled, both algae and solubilized MCs could be efficaciously removed by ultrasound-enhanced coagulation and electrocoagulation/electrooxidation.

Promoting effects of Fe_2O_3 to Pt electrocatalysts toward methanol oxidation reaction in alkaline electrolyte

Fe_2O_3 nanorods and hexagonal nanoplates were synthesized and used as the promoters for Pt electrocatalysts toward the methanol oxidation reaction（MOR） in an alkaline electrolyte.The catalysts were characterized by scanning electron microscopy,transmission electron microscopy,X-ray diffraction,X-ray photoelectron spectroscopy,cyclic voltammetry and chronoamperometry.The results show that the presence of Fe_2O_3 in the electrocatalysts can promote the kinetic processes of MOR on Pt,and this promoting effect is related to the morphology of the Fe_2O_3 promoter.The catalyst with Fe_2O_3 nanorods as the promoter（Pt-Fe_2O_3/C-R） exhibits much higher catalytic activity and stability than that with Fe_2O_3 nanoplates as the promoter（Pt-Fe_2O_3/C-P）.The mass activity and specific activity of Pt in a Pt-Fe_2O_3/C-R catalyst are 5.32 A/mgpt and 162.7 A/m^2_（Pt）,respectively,which are approximately 1.67 and 2.04 times those of the Pt-Fe_2O_3/C-P catalyst,and 4.19 and 6.16 times those of a commercial PtRu/C catalyst,respectively.Synergistic effects between Fe_2O_3 and Pt and the high content of Pt oxides in the catalysts are responsible for the improvement.These findings contribute not only to our understanding of the MOR mechanism but also to the development of advanced electrocatalysts with high catalytic properties for direct methanol fuel cells.

Dyes wastewater treatment by reduction-oxidation process in an electrochemical reactor packed with natural manganese mineral

A novel technology which combined electrochemical process catalyzed by manganese mineral with electro-assisted coagulation process was proposed in this study. The mineralization of organic pollutant from simulated dye wastewater containing an azo dye Acid Red B（ARB） was experimentally investigated using this method. It was found that the manganese mineral could catalyze the electrochemical process dramatically. The TOC removal percentage of electrochemical treatment catalyzed by manganese mineral was 43.6% while the TOC removal percentage of the process using the manganese mineral alone and using the electrolysis alone were 9.3% and 20.8%, respectively. Moreover, it was found that combined electroxidation with electro-assisted coagulation process could more effectively eliminate ARB. After a period of 180 min electrooxidation and 300 min electroreduction, almost 66.9% of TOC was removed, and the dissolved Mn^2＋. could be effectivly removed. The effects of the order of oxidation and reduction, the proper ratio electrooxidation/reduction time, and current density on the removal efficiency were investigated in detail. In addition, a proposed mechanism of manganese-mineral-catalyzed electrooxidation-reduction process was discussed in this paper.

Recent development of methanol electrooxidation catalysts for directmethanol fuel cell

Direct methanol fuel cells （DMFCs） are very promising power source for stationary and portable miniatureelectric appliances due to its high efficiency and low emissions of pollutants. As the key material, cata-lysts for both cathode and anode face several problems which hinder the commercialization of DMFCs.In this review, we mainly focus on anode catalysts of DMFCs. The process and mechanism of methanolelectrooxidation on Pt and Pt-based catalysts in acidic medium have been introduced. The influences ofsize effect and morphology on electrocatalytic activity are discussed though whether there is a size effectin MOP, catalyst is under debate. Besides, the non Pt catalysts are also listed to emphasize though Pt isstill deemed as the indispensable element in anode catalyst of DMFCs in acidic medium. Different cata-lyst systems are compared to illustrate the level of research at present. ome debates need to be verifiedwith experimental evidences.

Electrooxidation of Hydroxypivalaldehyde in an Undivided Cell

The factors affecting the electrooxidation of hydroxypivalaldehyde（HPAL） in an undivided cell were studied by using cyclic voltammetry（CV）, linear scan voltammetry（ LSV）, and potentiostatic electrolysis. The electrocatalytic activity and stability of a PbO2 electrode in sulfuric acid, acetic acid, and phosphoric acid were studied. The selectivity and the current efficiency for producing hydroxypivalic acid were explored with different supporting electrolytes, concentrations of HPAL, and pH values. The results show that higher selectivity and current efficiency for producing hydroxypivalic acid can be achieved when sulfuric acid with a high concentration is used as the supporting electrolyte and the selectivity and the current efficiency can reach 80% and 60%. resvectively.

N‐doped carbon modified Pt/CNTs synthesized by atomic layer deposition with enhanced activity and stability for methanol electrooxidation

A Pt/CNTs catalyst coated with N‐doped carbon（xNC‐Pt/CNTs） is synthesized by atomic layer dep‐osition（ALD） and applied in methanol electrooxidation reaction. Pt nanoparticles and polyimide（PI） are sequentially deposited on carbon nanotubes（CNTs） by ALD. After annealing at 600 °C in H2 atmosphere, the PI is carbonized to produce porous N‐doped carbon. Upon coating with a moder‐ately thick layer of N‐doped carbon, the optimized 50 NC‐Pt/CNTs show higher activity, better long‐term stability, and improved CO resistance towards methanol electrooxidation compared with Pt/CNTs and commercial Pt/C（20 wt%）. X‐ray photoelectron spectroscopy characterization result indicates that the Pt–CO bond is weakened after N‐doped carbon coating and CO adsorption on the Pt surface is weakened, leading to superior electrocatalytic performance.

Synergistic effect between few layer graphene and carbon nanotube supports for palladium catalyzing electrochemical oxidation of alcohols

Few layer graphene （FLG）, multi-walled carbon nanotubes （CNTs） and a nanotube-graphene composite （CNT-FLG） were used as supports for palladium nanoparticles. The catalysts, which were characterized by transmission electron microscopy, Raman spectroscopy and X-ray diffraction, were used as anodes in the electrooxidation of ethanol, ethylene glycol and glycerol in half cells and in passive direct ethanol fuel cells. Upon Pd deposition, a stronger interaction was found to occur between the metal and the nanotube-graphene composite and the particle size was significantly smaller in this material （6.3 nm）, comparing with nanotubes and graphene alone （8 and 8.4 nm, respectively）. Cyclic voltammetry experiments conducted with Pd/CNT, Pd/FLG and Pd/CNT-FLG in 10 wt% ethanol and 2 M KOH solution, showed high specific currents of 1.48, 2.29 and 2.51 mA-/zgp-d, respectively. Moreover, the results obtained for ethylene glycol and glycerol oxidation highlighted the excellent electrocatalytic activity of Pd/CNT-FLG in terms of peak current density （up to 3.70 mAgd for ethylene glycol and 1.84 mAfor glycerol, respectively）. Accordingly, Pd/CNT-FLG can be considered as the best performing one among the electrocatalysts ever reported for ethylene glycol oxidation, especially considering the low metal loading used in this work. Direct ethanol fuel cells at room temperature were studied by obtaining power density curves and undertaking galvanostatic experiments. The power density outputs using Pd/CNT, Pd/FLG and Pd/CNT-FLG were 12.1, 16.3 and 18.4 mW.cm-2, respectively. A remarkable activity for ethanol electrooxidation was shown by Pd/CNT-FLG anode catalyst. In a constant current experiment, the direct ethanol fuel cell containing Pd/CNT-FLG could continuously deliver 20 mA.cm-2 for 9.5 h during the conversion of ethanol into acetate of 30%, and the energy released from the cell was about 574 J.

Graphene-nickel nitride hybrids supporting palladium nanoparticles for enhanced ethanol electrooxidation

Electrocatalysts for ethanol oxidation reaction(EOR)are generally limited by their poor durability because of the catalyst poisoning induced by the reaction intermediate carbon monoxide(CO).Therefore,the rapid oxidation removal of CO intermediates is crucial to the durability of EOR-based catalysts.Herein,in order to effectively avoiding the catalyst CO poisoning and improve the durability,the graphene-nickel nitride hybrids(AG-Ni_(3)N)were designed for supporting palladium nanoparticles(Pd/AG-Ni_(3)N)and then used for ethanol electrooxidation.The density functional theory(DFT)calculations demonstrated the introduction of AG-Ni_(3)N depresses the CO absorption and simultaneously promotes the adsorption of OH species for CO oxidation removal.The fabricated Pd/AG-Ni_(3)N catalyst distinctively exhibits excellent electroactivity with the mass catalytic activity of 3499.5 m A mg^(-1) on EOR in alkaline media,which is around 5.24 times higher than Pd/C(commercial catalyst).Notably,the Pd/AG-Ni_(3)N hybrids display excellent stability and durability after chronoamperometric measurements with a total operation time of 150,000 s.

One step NaBH_4 reduction of Pt-Ru-Ni catalysts on different types of carbon supports for direct ethanol fuel cells : Synthe sis and characte rization

The ternary catalyst Pt75Ru5Ni20 was conducted on various types of carbon supports including functionalized Vulcan XC-72R(f-CB),functionalized multi-walled carbon nanotubes(f-MWCNT),and mesoporous carbon(PC-Zn-succinic)by sodium borohydride chemical reduction method to improve the ethanol electrooxidation reaction(EOR)for direct ethanol fuel cell(DEFC).It was found that the particle size of the metals on f-MWCNT was 5.20 nm with good particle dispersion.The alloy formation of ternary catalyst was confirmed by XRD and more clearly described by SEM element mapping,which was relevant to the efficiency of the catalysts.Moreover,the mechanism of ethanol electrooxidation reaction based on the surface reaction was more understanding.The activity and stability for ethanol electrooxidation reaction(EOR)were investigated using cyclic voltammetry and chronoamperometry,respectively.The highest activity and stability for EOR were observed from Pt75Ru5Ni20/f-MWCNT due to a good metal-carbon interaction.Ru and Ni presented in Pt-Ru-Ni alloy improved the activity and stability of ternary catalysts for EOR.Moreover,the reduction of Pt content in ternary catalyst led to the catalyst cost deduction in DEFC.

Recent advances in glycerol valorization via electrooxidation:Catalyst,mechanism and device

Glycerol is one of the most important biomass-based platform molecules,massively produced as a by-product in the biodiesel industry.Its high purification cost from the crude glycerol raw material limits its application and demands new strategies for valorization.Compared to the conventional thermocatalytic strategies,the electrocatalytic strategies can not only enable the selective conversion at mild conditions but also pair up the cathodic reactions for the co-production with higher efficiencies.In this review,we summarize the recent advances of catalyst designs and mechanistic understandings for the electrocatalytic glycerol oxidation(GOR),and aim to provide an overview of the GOR process and the intrinsic structural-activity correlation for inspiring future work in this field.The review is dissected into three sections.We will first introduce the recent efforts of designing more efficient and selective catalysts for GOR,especially toward the production of value-added products.Then,we will summarize the current understandings about the reaction network based on the ex-situ and in-situ spectroscopic studies as well as the theoretical works.Lastly,we will select some representative examples of creating real electrochemical devices for the valorization of glycerol.By summarizing these previous efforts,we will provide our vision of future directions in the field of GOR toward real applications.

Palladium Nanoparticles Loaded on Carbon Modified TiO_2 Nanobelts for Enhanced Methanol Electrooxidation

Carbon modified TiO_2 nanobelts(TiO_2-C) were synthesized using a hydrothermal growth method,as a support material for palladium(Pd) nanoparticles(Pd/TiO_2-C) to improve the electrocatalytic performance for methanol electrooxidation by comparison to Pd nanoparticles on bare TiO_2 nanobelts(Pd/TiO_2)and activated carbon(Pd/AC). Cyclic voltammetry characterization was conducted with respect to saturated calomel electrode(SCE) in an alkaline methanol solution, and the results indicate that the specific activity of Pd/TiO_2-C is 2.2 times that of Pd/AC and 1.5 times that of Pd/TiO_2. Chronoamperometry results revealed that the TiO_2-C support was comparable in stability to activated carbon, but possesses an enhanced current density for methanol oxidation at a potential of -0.2 V vs. SCE. The current study demonstrates the potential of Pd nanoparticle loaded on hierarchical TiO_2-C nanobelts for electrocatalytic applications such as fuel cells and batteries.

Fabrication of C@MoxTi1-xO2-δ nanocrystalline with functionalized interface as efficient and robust PtRu catalyst support for methanol electrooxidation

A core shell structured C@MoxTi1-xO2-δnanocrystal with a functionalized interface(C@MTNC-FI)was fabricated via the hydrothermal method with subsequent annealing derived from tetrabutyl orthotitanate.The formation of anatase TiO2 was inhibited by the simultaneous presence of the hydrothermal etching/regrowth process,infiltration of Mo dopants and carbon coating,which endows the C@MTNC-FI with an ultrafine crystalline architecture that has a Mo-functionalized interface and carbon-coated shell.Pt Ru nanoparticles(NPs)were supported on C@MTNC-FI by employing a microwave-assisted polyol process(MAPP).The obtained Pt Ru/C@MTNC-FI catalyst has 2.68 times higher mass activity towards methanol electrooxidation than that of the un-functionalized catalyst(Pt Ru/C@TNC)and 1.65 times higher mass activity than that of Pt Ru/C catalyst with over 25%increase in durability.The improved catalytic performance is due to several aspects including ultrafine crystals of TiO2 with abundant grain boundaries,Mofunctionalized interface with enhanced electron interactions,and core shell architecture with excellent electrical transport properties.This work suggests the potential application of an interface-functionalized crystalline material as a sustainable and clean energy solution.

Atomically dispersed catalysts for small molecule electrooxidation in direct liquid fuel cells

Direct liquid fuel cells(DLFCs) have received increasing attention because of their high energy densities,instant recharging abilities, simple cell structure, and facile storage and transport. The main challenge for the commercialization of DLFCs is the high loading requirement of platinum group metals(PGMs) as catalysts. Atomically dispersed catalysts(ADCs) have been brought into recent focus for DLFCs due to their well-defined active sites, high selectivity, maximal atom-utilization, and anti-poisoning property. In this review, we summarized the structure–property relationship for unveiling the underlying mechanisms of ADCs for DLFCs. More specifically, different types of fuels used in DLFCs such as methanol, formic acid,and ethanol were discussed. At last, we highlighted current challenges, research directions, and future outlooks towards the practical application of DLFCs.

Synthesis of Pt and Pt-Fe nanoparticles supported on MWCNTs used as electrocatalysts in the methanol oxidation reaction

This work reports a feasible synthesis of highly-dispersed Pt and Pt-Fe nanoparticles supported on multiwall carbon nanotubes （MWCNTs） without Fe and multiwall carbon nanotubes with iron （MWCNTs-Fe） which applied as electrocatalysts for methanol electrooxidation. A Pt coordination complex salt was synthesized in an aqueous solution and it was used as precursor to prepare Pt/MWCNTs, Pt/MWCNTs-Fe, and Pt-Fe/MWCNTs using FeC12.4H20 as iron source which were named S 1, S2 and S3, respectively. The coordination complex of platinum （TOA）2PtC16 was obtained by the chemical reaction between （NH4）2PtC16 with tetraoctylammonium bromide （TOAB） and it was characterized by FT-IR and TGA. The materials were characterized by Raman spectroscopy, SEM, EDS, XRD, TEM and TGA. The electrocatalytic activity of Pt-based supported on MWCNTs in the methanol oxidation was investigated by cyclic voltammetry （CV） and chronoamperometry （CA）. Pt-Fe/MWCNTs electrocatalysts showed the highest electrocatalytic activity and stability among the tested electrocatalysts due to that the addition of ＂Fe＂ promotes the OH species adsorption on the electrocatalyst surface at low potentials, thus, enhancing the activity toward the methanol oxidation reaction （MOR）.

Active sites contribution from nanostructured interface of palladium and cerium oxide with enhanced catalytic performance for alcohols oxidation in alkaline solution

Nanostructured interface is significant for the electrocatalysis process. Here we comparatively studied the electrooxidation of alcohols catalyzed by nanostructured palladium or palladium-cerium oxide. Two kinds of active sites were observed in palladium-cerium oxide system, attributing to the co-action of Pd-cerium oxide interface and Pd sites alone, by CO stripping technique, a structure-sensitive process generally employed to probe the active sites. Active sites resulting from the nanostructured interfacial contact of Pd and cerium oxide were confirmed by high resolution transmission electron microscopy and electrochemical CO stripping approaches. Electrochemical measurements of cyclic voltammetry and chronometry results demonstrated that Pd-cerium oxide catalysts exhibited much higher catalytic performances for alcohols oxidation than Pd alone in terms of activity, stability and anti-poisoning ability.The improved performance was probably attributed to the nanostructured active interface in which the catalytic ability from each component can be maximized through the synergistic action of bi-functional mechanism and electronic effect. The calculated catalytic efficiency of such active sites was many times higher than that of the Pd active sites alone. The present work showed the significance of valid nanostructured interface design and fabrication in the advanced catalysis system.

Positively charged carbon electrocatalyst for enhanced power performance of L-ascorbic acid fuel cells

Carbon surface with large oxygen and carbon ratio(O/C) indicated an outstanding electro-catalytic activity toward L-ascorbic acid oxidation, compared to platinum group metals. However, interrelation of surface functional groups and its electro-catalytic activity is still unclear. In this paper, we prepared different levels of oxidized carbons by a simple acid treatment and investigated the correlation between the surface oxygen functional groups of acid-treated carbon and electro-catalytic activity in an electrooxidation of L-ascorbic acid. Positively charged carbon was demonstrated by lone pair electron of oxygen from valence band spectra study. It was revealed that the positively charged carbon, especially involved in carbonyl, showed enhanced the electro-catalytic activity through both better adsorption of negatively charged reactants and lowered LUMO by electronegativity of oxygen.