钨基材料在电催化领域的应用进展

目前有关电催化剂应用的诸多研究领域，特别是商业领域，仍然由贵金属及其氧化物占据，但因其存在高成本和易中毒的壁垒而迫使科研人员把研究目光转向钨基电催化材料。氧化钨在制备条件得到有效控制的前提下可实现晶型结构及钨元素价态的多变，因此易于参加多种电化学反应，可实现对特定电化学反应的有效催化。回顾了不同晶相结构氧化钨基电极材料和不同异质结构钨基电极材料的制备方法、结构优势及其对各类电化学反应的优越催化性能，并从电极材料的制备和结构入手深入分析了文中所涉及电极材料优越催化性能的本质原因。以氧化钨及钨基电极材料的优越电催化性能为主线，辅以对电极材料的制备方法和特殊结构的分析，深入探讨了此类电催化材料的优势和发展方向，并总结本领域近5年的科研成果，为此类研究方向的深入开展提供了一定的借鉴经验。     

碳纳米管/铁氰化镍/聚苯胺杂化膜对抗坏血酸的电催化氧化

采用循环伏安一步共聚法在碳纳米管修饰的铂基体上制备了立方体的铁氰化镍/聚苯胺/碳纳米管杂化膜;采用循环伏安法和计时电流法测试了杂化膜对抗坏血酸的电催化氧化性能;通过扫描电子显微镜(SEM)观察了杂化膜电极的表观形貌。结果表明,该电极对抗坏血酸具有较高的电催化氧化活性;在0.1 mol/L PBS和0.1 mol/L KNO3的溶液中,该杂化膜电极对抗坏血酸的催化氧化电流与其浓度在1×10-5～1.4×10-4mol/L呈良好的线性关系,相关性系数R=0.996 6,检出限为6.09×10-6mol/L,同时具有较高的灵敏度754.8 mA.M-1.cm-2,并采用计时电流法对抗坏血酸催化氧化的扩散系数和催化速率常数进行了研究。     

热丝化学气相沉积制备BDD薄膜电极的电催化特性

研究了热丝化学气相沉积法(HFCVD)制备得到掺硼金刚石膜电极电催化氧化典型有机物苯酚的特性.Raman光谱测试显示制备BDD电极具有较好的金刚石相,循环伏安测试表明该电极具有较高的析氧过电位(+2.3V vsSCE).在电催化氧化苯酚过程中,化学需氧量(COD)能够有效去除,降解过程中有较高的电流效率,在COD较高的情况下,瞬时电流效率(ICE)可达100%,随着COD的降低ICE逐渐减少.催化实验结果表明,BDD电极是一种优良的电催化降解有机物新型电极.     

电催化氧化处理难降解废水用电极材料的研究进展

随着石油化工、医药等工业的迅速发展,工业废水中难降解物质与日俱增,采用传统的水处理方法已难以达到环保要求。电催化氧化技术主要利用电极表面产生的活性物质羟基自由基进行氧化降解,具有氧化能力强、无需添加化学药剂、无二次污染的优势,而且电催化氧化工艺操作简单、处理条件温和,在处理难降解废水方面具有诸多优势。电催化氧化技术的核心部件是阳极,因此阳极材料的开发一直是研究人员关注的重点。一般要求阳极材料具有析氧电位高、电催化活性高、耐腐蚀、稳定性好、价格低廉等特点。目前常用的阳极材料有钛基金属氧化物阳极(SnO_2电极和PbO_2电极)和合成掺硼金刚石薄层电极,但是这些材料存在使用寿命短、制作成本高等问题。通过改性制备复合金属氧化物阳极可以改善上述问题,常用的改性方法包括掺杂离子、引入中间层、掺杂纳米颗粒、调控电极材料的微观形貌等。改性可以提高电极电催化性能、导电性及稳定性,增大电极的反应面积,延长电极寿命。因此复合金属氧化物阳极的制备是阳极材料研究的重点。在二维电极的基础上引入粒子电极可以构成三维电极系统。在三维电极系统中,粒子电极在电场作用下,会极化形成一个个微型电解槽,极大地增加了反应面积。因而三维电极相比于二维电极具有面体比大、电催化效率更高、能耗更低的优势,因此高催化活性、高稳定性的粒子电极的研制成为了电催化氧化技术领域新的研究方向。目前,常用的粒子电极材料主要有碳材料(活性炭、炭气凝胶等)、金属氧化物(Al_2O_3、Fe_3O_4等)、陶瓷和矿物类等。本文从电催化氧化的机理以及三维电极的工作原理出发,综述了在电催化氧化处理废水中广泛应用的电极材料,包括钛基金属氧化物阳极、合成掺硼金刚石薄层电极,重点介绍了在三维电极系统中使用的粒子电极。并对今后废水处理中电催化氧化电极材料的研究趋势进行了展望,指出提高电催化氧化效率不仅需改进电极材料,还需改善反应器构型及与其他工艺的耦合等,以实现电催化氧化技术的推广应用。     

聚苯胺载铂电极对甲醛的电催化氧化

在金属Ti电极基体上,以循环伏安法聚合得到颗粒状聚苯胺修饰电极,以聚苯胺为Pt的载体,制备得到聚苯胺载铂电极(Pt/PAn/Ti),并通过扫描电镜和循环伏安法对该电极进行了表征。以Pt/PAn/Ti电极为阳极研究了甲醛在该电极上的氧化,结果表明,聚苯胺的存在使得铂微粒分散程度更好,有效面积更大,对甲醛的电催化氧化的电流密度达到77.2mA/cm2,是同样条件下没有聚苯胺电极的2.3倍。同时,该电极对甲醛的催化氧化效果与铂的沉积量有一定关系。     

石墨粉末化学镀Ni-P催化剂表面乙醇的电催化氧化

电催化乙醇氧化的阳极材料易失效.在活性炭(C活性)上化学沉积Ni-P颗粒,制备了Ni-P/C活性催化剂,将其填入213型铂电极凹槽之中,制成Ni-P/C活性电极.采用扫描电镜(SEM)和电化学循环伏安法对Ni-P/C活性催化剂性能进行了研究.结果表明:球状Ni-P颗粒以约为100 nm的大小均匀分布于C活性表面;仅C活性电极能催化乙醇发生氧化,但易失活,而Ni-P/C活性电极可以催化乙醇在-0.24 V发生氧化,在阴极极化扫描过程中,-0.39 V时会出现乙醇氧化中间物的氧化峰,催化乙醇氧化的峰电流随循环使用次数的增加而提高,氧化电位逐渐负移,这与Ni-P在碱性条件下电氧化产生Ni(OH)2和NiOOH有关.     

钛基Co中间层SnO2电催化电极的制备及性能研究

为提高钛基二氧化锡电极的稳定性,设计并制备了含Co中间层的钛基二氧化锡电催化电极Ti/Co/SnO2,以苯酚为目标有机物,考察了所制备Ti/Co/SnO2电极电催化氧化降解苯酚的性能,并采用SEM、EDX以及XPS等检测方法分析了Ti/Co/SnO2电极表面的形貌、元素组成及元素化学态.研究结果表明,含有中间层的Ti/Co/SnO2电极其使用寿命较不含中间层的钛基二氧化锡电极Ti/SnO2大幅度提高,但其对苯酚的电催化降解活性有所下降,氧化还原电对Co2 /Co3 的存在是所制备Ti/Co/SnO2电极稳定性及电催化活性改变的主要原因.     

TiO2纳米管阵列催化降解甲基橙的性能研究

采用阳极氧化法制备了TiO2纳米管阵列电极,以甲基橙为目标降解物研究了TiO2纳米管阵列电极的光催化和光电催化性能.此外,还进行了超声辐射替代紫外光照探索性研究.结果表明,阳极氧化时间和热处理温度对TiO2纳米管阵列电极的光催化性能具有显著影响;在光催化过程中,施加一定外加电压可有效提高电极的光催化活性.尽管与紫外光照相比,超声辐射在TiO2纳米管阵列电极的催化氧化甲基橙分子过程中的促进作用具有一定的差距,但仍显示出替代紫外光照的可行性.     

铂钌/聚苯胺/聚砜复合膜电极的制备及对甲醇的电催化氧化

利用电化学聚合分别制备了铂(Pt)及其铂钌(PtRu)/聚苯胺(PAN)/聚砜(PSF)复合膜电极。采用循环伏安法和电化学交流阻抗对复合膜电极的甲醇电催化氧化性能进行了比较与分析。结果表明:PtRu/PAN/PSF电极对甲醇的电催化活性比Pt/PAN/PSF电极的高,铂钌的沉积不仅改变了催化剂表面对氢的吸附性质,而且使氧化物还原峰电位向阴极方向移动。另外,对在不同浓度下沉积的铂钌电极对甲醇的催化效果也做了讨论,验证了RPt∶Ru=2∶1时,复合膜电极具有最好的催化活性。     

Ti／SnO2＋Sb2O3／PbO2电极的电催化性

本文研制了一种阳极－Ｔｉ／ＳｎＯ２＋Ｓｂ２Ｏ３／ＰｂＯ２，考察了该电极在２．５ＭＨ２ＳＯ４中不同温度下的电解使用寿命，测定了该电极的极化曲线和电化学动力学参数ａ、ｂ、ｉ。讨论了ＰｂＯ２电极的析氧机理和酚氧化的催化性，结果表明该电极的电催化性能优良。     

Anaerobic ammonia removal in presence of organic matter: a novel route

This study describes the feasibility of anaerobic ammonia removal process in presence of organic matter. Different sources of biomass collected from diverse eco-systems containing ammonia and organic matter (OM) were screened for potential anaerobic ammonia removal. Sequential batch studies confirmed the possibility of anaerobic ammonia removal in presence of OM, but ammonia was oxidized anoxically to nitrate (at oxidation reduction potential; ORP=-248+/-25 mV) by an unknown mechanism unlike in the reported anammox process. The oxygen required for oxidation of ammonia might have been generated through catalase enzymatic activity of facultative anaerobes in mixed culture. The oxygen generation possibility by catalase enzyme route was demonstrated. Among the inorganic electron acceptors (NO(2)(-), NO(3)(-) and SO(4)(2-)) studied, NO(2)(-) was found to be most effective in total nitrogen removal. Denitrification by the developed culture was much effective and faster compared to ammonia oxidation. The results of this study show that anaerobic ammonia removal is feasible in presence of OM. The novel nitrogen removal route is hypothesized as enzymatic anoxic oxidation of NH(4)(+) to NO(3)(-), followed by denitrification via autotrophic and/or heterotrophic routes. The results of batch study were confirmed in continuous reactor operation.     

Ammonia removal in electrochemical oxidation: mechanism and pseudo-kinetics

This paper investigated the mechanism and pseudo-kinetics for removal of ammonia by electrochemical oxidation with RuO(2)/Ti anode using batch tests. The results show that the ammonia oxidation rates resulted from direct oxidation at electrode-liquid interfaces of the anode by stepwise dehydrogenation, and from indirect oxidation by hydroxyl radicals were so slow that their contribution to ammonia removal was negligible under the condition with Cl(-). The oxidation rates of ammonia ranged from 1.0 to 12.3 mg N L(-1)h(-1) and efficiency reached nearly 100%, primarily due to the indirect oxidation of HOCl, and followed pseudo zero-order kinetics in electrochemical oxidation with Cl(-). About 88% ammonia was removed from the solution. The removed one was subsequently found in the form of N(2) in the produced gas. The rate at which Cl(-) lost electrons at the anode was a major factor in the overall ammonia oxidation. Current density and Cl(-) concentration affected the constant of the pseudo zero-order kinetics, expressed by k=0.0024[Cl(-)]xj. The ammonia was reduced to less than 0.5 mg N L(-1) after 2h of electrochemical oxidation for the effluent from aerobic or anaerobic reactors which treated municipal wastewater. This result was in line with the strict discharge requirements.     

Fate of ammonia in the atmosphere--a review for applicability to hazardous releases

The physical and chemical mechanisms responsible for the removal of ammonia from the atmosphere have been reviewed. Capture by atmospheric moisture (clouds, rain, fog), surface water (rivers, lakes, seas), and deposition on vegetation and soil constitute the main pathways for ammonia removal from the troposphere. Ammonia catalyzes the atmospheric oxidation of sulfur dioxide to sulfur trioxide and reacts rapidly with acidic components of the atmosphere (sulfuric, nitric, and hydrochloric acids). The ammonium salts formed are the main components of smog aerosols and thus affect the opacity of the atmosphere and the earth radiation budget. Slow oxidation of ammonia in the atmosphere plays only a minor role in its removal. The data obtained for ammonia reactions under normal atmospheric conditions are generally applicable to model chemical reactions occurring during massive release of ammonia in the atmosphere, provided the impact of high ammonia concentration on the mass transfer processes that control some of these reactions, are taken into account.     

催化剂选择性催化氧化NH3的新进展

在处理含NH_3的工业废气方面,氨选择性催化氧化法(NH_3-SCO)一直是研究热点。在讨论氨选择性催化氧化法(NH_3-SCO)反应机理的基础上,重点综述了关于选择性催化氧化NH_3的5种催化剂:贵金属催化剂、过渡金属催化剂、分子筛载体催化剂、复合氧化物催化剂及整体催化剂的最新研究进展,并对未来NH_3-SCO的发展进行了展望。     

Polycrystalline ZnO-In2O3 thin films as gas sensors

Polycrystalline ZnO-In₂O₃ thin films were prepared by thermal oxidation in air of metallic Zn-In films deposited onto glass substrates by thermal evaporation under vacuum. Different oxidation conditions (oxidation temperature, oxidation time, heating rate) were used in order to prepare homogeneous films that can be used as gas sensors. Polycrystalline structure of the as-obtained films was confirmed by X-ray and electron diffraction investigations. The electrical conductivity of various thin film samples ranged between 0.84 and 6.44 (Ω cm)^− 1.Gas sensitivity to six different gasses (ammonia, methane, LPG, acetone, ethanol and formaldehyde) was evaluated and it was found that the highest sensitivity was obtained for ammonia.     

Effect of potential electron acceptors on anoxic ammonia oxidation in the presence of organic carbon

A novel route of anoxic ammonia removal in the presence of organic carbon was identified recently from ecosystems contaminated with ammonia. Sequencing batch reactor (SBR) studies were carried out in anoxic condition at oxidation–reduction potential varied from −185 to −275 mV for anoxic ammonia oxidation with adapted biomass (mixed culture). SBR studies were carried out in absence and in the presence of externally added organic carbon and/or in the presence of inorganic electron acceptors like NO₂⁻, NO₃⁻ and SO₄²⁻. The results showed anoxic ammonia oxidation to nitrate (in contrast to reported anammox process) in the presence of organic carbon available through endogenous respiration whereas anoxic ammonia oxidation was effective in the presence of externally added organic compound for nitrogen removal. The presence of externally added inorganic electron acceptors like NO₂⁻, NO₃⁻ and SO₄²⁻ was effective in anoxic ammonia oxidation, but failed to follow the reported anammox reaction's stoichiometry in nitrogen removal in the presence of organic carbon. However, the presence of NO₂⁻ affected best in total nitrogen removal compared to other electron acceptors and maximum ammonia removal rate was 100 mg NH₄⁺/g MLVSS/d. Based on the results, it is possible to suggest that rate of anoxic ammonia oxidation depends up on the respiration activities of mixed culture involving organic carbon, NO₂⁻, NO₃⁻ and SO₄²⁻. The process shows possibilities of new pathways of ammonia oxidation in organic contaminated sediments and/or wastewater in anoxic conditions.     

Catalytic wet oxidation of ammonia solution: activity of the nanoscale platinum-palladium-rhodium composite oxide catalyst

Aqueous solutions of 400-1000 mg/L of ammonia were oxidized in a trickle-bed reactor (TBR) in this study of nanoscale platinum-palladium-rhodium composite oxide catalysts, which were prepared by the co-precipitation of H(2)PtCl(6), Pd(NO(3))(3) and Rh(NO(3))(3). Hardly any of the dissolved ammonia was removed by wet oxidation in the absence of any catalyst, whereas about 99% of the ammonia was reduced during wet oxidation over nanoscale platinum-palladium-rhodium composite oxide catalysts at 503 K in an oxygen partial pressure of 2.0 MPa. A synergistic effect exists in the nanoscale platinum-palladium-rhodium composite structure, which is the material with the highest ammonia reduction activity. The nanometer-sized particles were characterized by TEM, XRD and FTIR. The effect of the initial concentration and reaction temperature on the removal of ammonia from the effluent streams was also studied at a liquid hourly space velocity of under 9 h(-1) in the wet catalytic processes.     

Electrochemical Ammonia Synthesis and Ammonia Fuel Cells

Ammonia is a promising platform molecule for the future renewable energy infrastructure owing to its high energy density (when liquefied) and carbon‐free nature. In particular, the interconversion between the chemical and electrical energies leveraging the nitrogen cycle could be an effective approach in mitigating the intermittency of renewable electricity production. However, efficient methods to store and release energy into and from ammonia, respectively, are still under development. Here, the latest developments in electrochemical ammonia synthesis and ammonia fuel cells are presented, and perspectives in the technical challenges and possible remedies are outlined. N₂ electrolysis, plasma‐enabled N₂ activation, and electro‐thermochemical looping are three potential approaches for electrochemical ammonia synthesis; however, achieving high selectivity and energy efficiency remains challenging. Direct ammonia fuel cells are suitable for a broad range of mobile and transportation applications but are limited by the lack of active catalysts for ammonia oxidation.     

碳酸氢铵电化学氧化阳极对含油海底沉积物微生物燃料电池性能影响及其加速降解研究

制备了3种阳极(未改性阳极、氨水改性阳极、NH_4HCO_3电化学氧化改性阳极)组建海底沉积物微生物燃料电池(MSMFCs),探究阳极的不同氨改性方法对含油MSMFCs电化学性能和石油降解率的影响。结果表明,电化学氧化改性阳极的电容特性是未改性阳极组的1.78倍,并且其抗极化能力最强,交换电流密度为2.57×10~(-2)A·m~(-2),是未改性的5.00倍;由电化学氧化改性阳极组建的电池的最大输出功率密度是1.53×102m W·m~(-2),较空白组的增加3.56倍,且该电池阳极沉积物中石油的降解率是空白组的10.40倍,这是因为改性阳极表面连入了有利于微生物附着的酰胺基团和氨基基团,提高了电池电化学性能并加速了石油的降解。     

Steady-state voltammetry of hydroxide ion oxidation in aqueous solutions containing ammonia

An oxidation process observed in dilute aqueous solutions of ammonia was investigated under steady-state conditions with gold microelectrodes with radii in the range 2.5-30 microm. Over the ammonia concentration range 0.1-10 mM, a well-defined voltammetric wave was observed at approximately 1.4 V versus Ag/AgCl. It was attributed to the oxidation of hydroxide ions that arise from the dissociation of the weak base. The steady-state limiting current was found to depend on the concentration of supporting electrolyte, and in solution with low electrolyte, it was enhanced by migration contribution, as expected for a negatively charged species that oxidizes on a positively charged electrode. In addition, the steady-state limiting current was proportional to both the ammonia concentration and the electrode radius. The overall electrode process was analyzed in terms of a CE mechanism (homogeneous chemical reaction preceding the heterogeneous electron transfer) with a fast chemical reaction when measurements were carried out in solutions containing NH3 at < or = 5 mM and with electrodes having a radius of > or = 5 microm. This was ascertained by comparing experimental and theoretical data obtained by simulation. The formation of the soluble complex species Au(NH3)2+ was also considered as a possible alternative to explain the presence of the oxidation wave. This process however was ruled out, as the experimental data did not fit theoretical predictions in any of the conditions employed in the investigation. Instead, the direct oxidation of NH3, probably to N2O, was invoked to explain the anomalous currents found when the CE process was strongly kinetically hindered. Throughout this study, a parallel was made between the CE mechanism investigated here and that known to occur during the hydrogen evolution reaction from weak acids.