RCEES OpenIR  > 环境水质学国家重点实验室
电催化氧化降解污染物协同析氢效能与机制研究
Alternative TitleEffectiveness and Mechanism Research on Electrocatalytic Oxidative Degradation of Contaminant s and S ynergistic H ydrogen Generation
张凯
Subtype博士
Thesis Advisor刘会娟 ; 张弓
2019-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name工学博士
Degree Discipline环境工程
Keyword电催化,氢能源,电极材料,连续流反应器,废水处理 electrocatalysis, h Ydrogen Energy, e Lectrode Materials, c Ontinuous Flow Reactor , w Astewater Treatment
Abstract

      实现污染物定向降解转化 同时 高效 回收 能源 是解决 环境问题 和 能源危机 的有效 途径 。 氢是一种清洁,环保无污染的能量载体。 高焓污染物具有 易于氧化转化电位低 的 特性 。利用高焓污染物的氧化 降解 来代替 电催化分解 水 的 产 氧过程 不仅 可 实现了污水的有效净化,同时还 能产生 清洁的 氢 能源 。 如何提高电极的转化降解效率和开发高效节能的反应器 装置 是解决 电催化技术推广应用 的关键问题。 因此, 以含氮污染物为例, 本 文 研究了 廉价 高活性阴极 阳极 材料电极的 制备 和高效污水净化反应器的开发 并重点 关注 了 含氮 污染物 在电极 表面水相界面 的 迁移转化 降解过程以及 电催化析 氢的效能与机制 。
      (1) 利用水热 高温煅烧法,制备出一种混相 碳化钼 Mo 2 C )催化 阴 极并应用于电解水 析 氢的研究 。 发现 在 混相碳化钼的 制备 过程 中, 调节钨的含量可 实现碳化钼从 α 相向 β 相 的 转变。 热重 示差扫描量热法( TG DSC 分析结果表明 增加钨含量来提高 Mo C 键形成所需的温度, 是 实现 α Mo 2 C 向 β Mo 2 C转变的关键 。 受益于最佳的 Mo C 键长 、 大的表面积和丰富的活性位点( Mo 2+具有最佳钨添加量的 混相 碳化钼纳米 电极( 0.5 W Mo x C 表现 出优异的 电催化活性和稳定性。 与纯 的 α Mo 2 C 和 β Mo 2 C 相比, 混相碳化钼电极 在 0.5 M H 2 SO 4和 1.0 M KOH 电解液中 分别需要过电位 148 和 93 mV 就能 驱动 20 mA cm 2 的析氢 电流密度。
      (2) 通过热解的方法引入 B 元素制备 出 具有氧空位的氧化钴( CoO )纳米线电极 ,并应用于电解水产氧反应的研究 。 密度泛函理论( DFT )计算预测硼( B )的掺入有利于过渡金属氧化物中氧空位的产生。结合 X 射线光电子能谱 ,拉曼和 电子顺磁共振光谱证实了氧缺陷的存在。近边结构 X 射线吸收光谱XANES )进一步研究发现 CoO 中的氧空位主要来源于 B 掺杂引起局部结构
的无序化。 DFT 计算结果进一步揭示了 *OOH 的氧化是丰富氧空位 CoO 析氧反应( OER )的限速步骤,并且氧空位的存在可以有效地降低破坏 Co O 键的反应势垒,从而有助于提高 OER 动力学。 因此 ,在碱性条件下,丰富氧空位的CoO电极在 280 mV 的低过电位下可驱动 10 mA cm 2 的电流密度。
      (3) 鉴于 电解水产氧反应 缓慢 的动力学和高的反应 势垒 ,本文利用 高焓含氮 污染物氧化降解来替代传统的 产氧反应 并 开发了高效 产 氢协同污染物降解的 连续流反应器 。 高分辨透射电镜( HRTEM )显示污染物降解过程 中 原位改变了磷化镍表面的活性物种。 X 射线光电子能谱和原位拉曼光谱证实理想价态Ni III 金属氧化物的形成导致尿素的有效降解。这有利于加速阳极电极和电解质界面的电荷转移, 因而 可实现低电压下污染物的连续降解和能源氢气的持续产生,并以此为基础,构建了一种穿透式连续流反应器。电压为 1. 5 0 V 时,在含尿素和 无尿素 的溶液中, 可 分别驱动电流 31.3 和 6.3 mA ,而电压增加到 1.70 V时,电流可达到 150 和 40 mA 。在电量通过 578 C 后, 尿素 氧化 降解的 去除 效率达到 79.6 。
       (4) 利用电池充放电原理, 以磷化钴 阵列多孔 电极作为 充放电 调节器, 在时间上 有效地分离了电解池中的 阴极 析氢 和 阳极 污染物降解 反应, 可 实现持续充电产氢 、 快速放电去污的 功效,从而达到 无膜 分离 H 2 的目的 。 基于此,研发出一种无膜 高效氢气 分离 和污染物降解 电解槽 装置 。 在 该 电解槽 装置 中, CoP电极 的高电容性可持久的 分离 H 2 ,在 平均电压 1.38 V 驱动 10 mA cm 2 的电流密度下, H 2 分离 时间可达到 1500 s ,几乎是纯 CoP 480s )的 3.1 倍。可以选择的是,存储在 CoP 纳米阵列中的能量可以通过与 NiSe 阳极的快速氨氮污染物降解耦合而消耗掉。凭借此,仅需要 1.55 V 的总电压就可驱动含氨污染物溶液中 10 mA cm 2 的电流密度,比在碱性条件下低了 0.14 V 。

Other Abstract

       Achieving degradation and conversion of targeted contaminant s and simultaneous ly obtaining energy is an effective way to solve environmental problems and energy crises. Hydrogen is a clean, environmentally friendly,non polluting and renewable energy carri er. High enthalpy contaminants possess the characteristics of easy oxidation and low conversion potential. T he substitution of contaminant degradation in wastewater for the water splitting not only achieves effective purification of wastewater , but also produces green hydrogen energy. How to improve the conversion and degradation efficiency of the electrode and develop a highly efficient and energy saving electrochemical apparatus is a key issue to solve the popularization and application of el ectrocatalytic technology. Therefore, taking nitrogenous pollutants as an example, this paper studies the preparation of inexpensive high activity cathode/anode material electrodes and the development of high efficiency wastewater purification reactors, an d f ocus on the migration,transformation and degradation process of nitrogenous contaminants at the electrode water phase interface and the efficiency and mechanism of electrocatalytic hydrogen evolution
          (1) A polycrystalline molybdenum carbide (Mo 2 C) electrode was prepared via hydrothermal calcination method and applied to the mechanism research of hydrogen evolution . The synthesis process of polycrystalline molybdenum carbide found that tuning additive (tungsten) context could realize the transform ation of molybdenum carbide from α phase to β phase. Thermogravimetry differentialscanning calorimetry (TG DSC) indicate ed that the increasing the amount of tungsten to elevate the temperature required for Mo C bond formation was a critical factor affecti ng the phase transformation of molybdenum carbide . Benefiting from the optimal Mo C bond length s , large surface area and abundant active sites, the polycrystalline molybdenum carbide electrode with optimal tungsten addition exhibited excellent electrocatal ytic activity and stability in the HER Compared with pure α Mo 2 C and β Mo 2 C, the polycrystalline molybdenum carbide electrode only required an overpotential of 148 and 93 mV to drive the current density of 20 mAcm 2 in 0.5 M H 2 SO 4 and 1.0 M KOH electrolyte, respectively.
       (2)C obalt oxide CoO nanowire electrode s with OVs are prepared via incorporation of B using a facile pyrolysis strategy and applied to the mechanism research of oxygen evolution Density functional theory (DFT) c alculations predict ed that the incorporation of boron (B) facilitates the generation of oxygen vacancies ( in the transition metal oxide. X ray photoelectron spectroscopy, Raman spectroscopy and electron paramagnetic resonance spectroscopy confirmed th e presence of oxygen vacancies. X ray absorption spectroscopy (XANES) of the near edge structure further found that oxygen vacancies in CoO were mainly derived from the disordering of the local structure caused by B doping. DFT calculation results further reveal ed that the oxidation of *OOH was the rate limiting step for OVs enriched CoO in the OER and that the presence of OVs could effciently lower the reaction barrier for breaking Co O bond, contributing to the improvement of OER kinetics. As expected, the OVs enriched CoO exhibits a low overpotential of 280 mV to reach the current density of 10 mA cm 2 under basic conditions.
       (3)In view of the sluggish kinetics and high reaction potential of oxygen evoluiton in the decompositon of water , t he oxidative degradation of high enthalpy containtants in wastewater is employed to replac e the traditional water oxidation .Furthermore, a conti nuous flow reactor with high efficiency hydrogen production and simultaneous contaminants degradation is developed . High resolution transmission electron microscopy (HRTEM) show ed that the active species on the surface of nickel phosphide were in situ generated during the degradation process of pollutants. Based on X ray photoelectron spectroscopy (XPS) and in situ Raman spectroscopy, we confirmed that the formation of the desired oxidation state of Ni IIIaccounted for the efficient urea degradation. The scenario was beneficial for accelerating charge transfer across the interface between the anode and electrolyte,thereby achieving synchronous degradation of pollutants and generation of energy hydrogen at low voltage , whereby a continuous flow reactor was constructed. A voltage of only 1. 5 0 V supported currents of 31.3 and 6. 5 mA in urea containing or not solutions, respectively, which reached 150 and 35 mA after the voltage was increased to 1.70 V, several times higher than that under basic conditions. After the discharge of 578 C, the removal efficiency for urea degradation reached 79.6%.
      (4)Using the principle of battery charge and discharge, the cobalt phosphide electrode is used as a charge and discharge mediator to effectively separate the cathode hydrogen evolution and anode pollutant degradation reaction in the electrolytic cell in time, thereby achieving the efficacy of persistent charg e hydrogen evolution and rapid discharge decontamination and the purpose of membrane free separation of H 2 . Based on this, a high efficiency membrane free hydrogen separation and contaminant degradation electrolyzer apparat us was developed In the
electrolytic cell device, the high capacitance of the CoP NAs mediator supported persistent H 2 seperation , where the H 2 production period achieved 1500 s at acurrent density of 10 mA cm 2 , almost 3.1 times longer than that for pure CoP (480s).Alternatively, the energy stored in the mediator could be exhausted via coupling with the oxidation of ammonia with NiSe as the anode . a total driving voltage of 1.55 V was required to support a current density of 10 mA cm 2 in the ammonia containing solution, ~0.14 V lower than that under basic conditions

Pages146
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/42348
Collection环境水质学国家重点实验室
Recommended Citation
GB/T 7714
张凯. 电催化氧化降解污染物协同析氢效能与机制研究[D]. 北京. 中国科学院生态环境研究中心,2019.
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