摘要
Electrochemical CO_(2)reduction reaction(CO_(2)RR)driven by sustainable energy has emerged as an attractive route to achieve the target of carbon neutral.Formate is one of the most economically viable products,and electrocatalytic CO_(2)RR to formate is a promising technology.High-pressure H-cell electrolyzer is easy to operate and allows high CO_(2)solubility for realizing high current density,but the design of highly efficient catalysts for working under high CO_(2)pressures remains challenging.Bismuth-based catalysts exhibit high formate selectivity,but suffer from limited activity.Here,we report a high-performance catalyst,which is derived from BiPO_(4)nanopolyhedrons during electrocatalytic CO_(2)RR to formate in neutral solution under high CO_(2)pressures.A high partial current density of formate(534 mA cm^(−2))and formate formation rate(9.9 mmol h^(−1) cm^(−2))with a formate Faradaic efficiency of 90%have been achieved over BiPO_(4)-derived catalyst at an applied potential of−0.81 V vs.RHE under 3.0 MPa CO_(2)pressure.We discover that BiPO_(4)nanopolyhedrons evolve into metallic Bi nanosheets with rich grain boundaries in electrocatalytic CO_(2)RR under high CO_(2)pressures,and the grain boundaries of the BiPO_(4)-derived catalyst play a vital role in promoting electrocatalytic CO_(2)RR to formate.Our theoretical studies reveal that the charge redistribution occurs at the grain boundaries of Bi surface,and this promotes CO_(2)activation and increases HCOO^(*)intermediate stability,thus making the pathway for CO_(2)RR to formate more selective and energy-favorable.This work not only demonstrates a highly efficient catalyst for CO_(2)RR to formate but also discovers a unique feature of catalyst evolution under high CO_(2)pressures.
可再生能源驱动的电催化还原CO_(2)制化学品和燃料是实现碳中和目标十分具有吸引力的技术.在电催化还原CO_(2)产物中,综合考虑产物的经济价值和还原所需能量,甲酸是最可行的产物之一.甲酸用途十分广泛,不仅可以用于生产各种高值化学品,还可作为氢的载体用于燃料电池.目前发展的电催化还原CO_(2)制甲酸或甲酸盐的催化剂主要有Pd,Cd,Hg,Sn,In,Tl,Pb和Bi等,其中Bi基催化剂具有价廉、环境友好和选择性高等特点.此外,电解器的结构也是影响反应性能的关键因素.传统的常压H池中,由于CO_(2)溶解度低和扩散限制,反应电流密度很难超过100 mA cm^(−2).流动池和膜电极反应器体系由于使用气体扩散电极,可以避免CO_(2)溶解度低的问题,获得较高的反应电流密度,但依然存在反应器结构复杂难控等问题.高压H池操控简单,而且可以使大量的CO_(2)溶解于溶液中,已有研究证明在高压H池中可以获得超过100 mA cm^(−2)的反应电流密度.同时,有研究发现,CO_(2)的压力会显著影响铜基催化剂上产物的选择性.然而,目前对高压H池中电催化还原CO_(2)的研究较少.因此,进一步设计高压条件下电催化还原CO_(2)制甲酸的高效催化剂,并研究其独特规律,具有重要意义.本文通过简单的一步水热方法合成了BiPO_(4)纳米多面体,并在高压H池中系统研究了其电催化还原CO_(2)制甲酸盐的性能.实验发现,BiPO_(4)纳米多面体衍生的催化剂(BiPO_(4)-derived)在高压H池中具有很高的活性.在CO_(2)压力为3.0 MPa的KHCO_(3)溶液中,控制阴极电位为−0.81 V vs.RHE,电催化还原CO_(2)制甲酸盐的法拉第效率为90%,甲酸盐部分电流密度可达534 mA cm^(−2),甲酸盐生成速率为9.9 mmol h^(−1) cm^(−2).X射线衍射、扫描电子显微镜、高分辨透射电子显微镜、循环伏安等表征结果表明,BiPO_(4)纳米多面体在高压CO_(2)还原反应条件下会演变成具有丰�
基金
国家科技部重点研发计划(2019YFE0104400)
国家自然科学基金(22022201,21972115,22121001)
福建省嘉庚创新实验室(RD2020020201).
