Non-precious Co3O4-TiO2/Ti cathode based electrocatalytic nitrate reduction: Preparation, performance and mechanism
Non-precious Co3O4-TiO2/Ti cathode based electrocatalytic nitrate reduction: Preparation, performance and mechanism
复制标题
非贵金属Co3O4-TiO2/Ti阴极电催化硝酸盐还原：制备、性能和机理
DOI：
10.1016/j.apcatb.2019.05.016
复制
发表时间：
2019-10-05
影响因子：
22.1
通讯作者：
Oturan, Mehmet A.
中科院分区：
文献类型：
--
作者：
Gao, Jianan;Jiang, Bo;Oturan, Mehmet A.
天然水体中存在高浓度的硝酸盐(NO3-)，对环境和人类健康构成严重威胁。因此，开发低成本、稳定的非贵金属催化剂以实现高效的硝酸根还原迫在眉睫。本研究采用溶胶-凝胶法和焙烧法相结合的方法制备了Co3O4-TiO2/Ti正极材料，并对其电催化还原NO3-的性能进行了评价。在包覆液中加入PVP可以改善Co3O4催化剂粒子的分散性。锐钛矿相的存在可以有效地稳定Co3O4，防止有毒的Co离子释放到溶液中。在500℃焙烧温度下，经4次镀膜即可制得NO3-还原性能最佳的Co3O4-TiO2TiO4正极材料。在溶液pH值3.0~9.0范围内，溶液pH值对NO3-的电催化还原影响不大，而电流密度从2.5 mA·cm(2)增加到25 mA·cm(2)则有利于NO3-的电催化还原。氨离子是硝酸根离子还原的主要最终产物，而氯离子的存在能够通过电化学反应生成活性氯物种而将铵离子氧化为N-2。电化学分析、清除实验和密度泛函理论计算共同证实了NO3-还原主要是由Co2+-Co3+-Co2+氧化还原过程引起的，而不是直接由阴极产生的电子引起的。与贵金属(如Pd和Ag)催化反应体系不同，在目前的Co3O4电催化反应过程中，原子H*更有利于通过Heyrovsky和Tafel途径转化为H-2，因此对NO3-还原的贡献较小。总之，本研究为设计稳定、经济的硝酸根还原阴极提供了新的范式。
The presence of high nitrate (NO3-) concentration in natural water constitutes a serious issue to the environment and human health. Therefore, the development of low-cost, stable non-precious metal catalysts is imminent for efficient NO3- reduction. In this study, we prepared a Co3O4 -TiO2/Ti cathode via combining sol-gel and calcination methods and evaluated its performance for electrocatalytic NO3- reduction. The dispersion of the Co3O4 catalyst particles was improved by the addition of PVP to the coating liquid. The presence of anatase could effectively stabilize Co3O4 and prevent the releasing of toxic Co ions into the solution. The Co3O4-TiO2/Ti cathode with the optimized performance for NO3- reduction could be prepared by four times coating at calcination temperature of 500 degrees C. The electrocatalytic reduction of NO3- was negligibly impacted by solution pH in the range of 3.0-9.0, while it could be facilitated by elevating the current density from 2.5 to 25 mA cm(2). Ammonium ions were the main final NO3- reduction product, and the presence of Cl- was capable to oxidize ammonium ions to N-2 due to the electrochemical production of reactive chlorine species. The electrochemical analyses, scavenging experiments and density functional theory calculations collectively confirm that NO3- reduction was mainly induced by the Co2+-Co3+-Co2+ redox process instead of being directly resulted from the electrons generated at the cathode. Unlike noble metal (e.g., Pd and Ag) based catalytic reaction systems, in the present Co3O4 mediated electrocatalytic reaction process, atomic H* would more favorably turn to H-2 by Heyrovsky and Tafel routes and therefore contributed marginally to the NO3- reduction. Generally, this study provided a new paradigm for designing the stable and cost-effective cathode for NO3- reduction.