Electrochemical CO2 reduction reaction (CO2RR) provides an economically viable method for converting green energy into valuable chemical feedstocks and fuels. Great progress has been made in the understanding and synthesis of oxidation-based precatalystsHowever, the dynamic changes in their local structure under operating conditions still hinder their further application. Here it isYang Huagui, Liu Pengfei, East China University of Science and Technology, Jiang Zheng, Shanghai Synchrotron Radiation Light Source, etcA molecularly twisted Bi2CuO4 precatalyst for efficient conversion of CO2 to formate is reported.
X-ray absorption fine structure (XAFS) results and theoretical calculations show that the twisted structure with molecular [CuO4]6-unit rotation is more conducive to the structural stability of the sample. Opera XAFS and Scanning Transmission Electron Microscopy (STEM) results have demonstrated that a considerable amount of lattice oxygen can be retained in the distorted sample after CO2RR. Electrochemical measurements of the distorted sample showed excellent activity and selectivity, with a very low overpotential of -400 mV of 194High formate partial current density of 6 mA cm-2. Further in-situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) calculations show that the retained oxygen can optimize the adsorption of *OCHO intermediates, thereby improving CO2RR performance.
DFT calculations were also used to explore the mechanism of HCOOH formation and the role of oxygen retention. Based on the experimental information, we constructed representative BI-CU and BI-O-CU models based on BI(012), as shown in Figure S20. The mechanism of CO2RR was first investigated, and by comparing the Gibbs free energy of different reaction steps (Fig. 5b and Fig. S21), we confirmed that Bi-O-Cu can maintain high selectivity for the conversion of CO2 to formate. Two formate formation mechanisms (Figure 5b) were then considered:(i)*CoOH mechanisms, i.e., *+CO2+ H+ E-Cooh + H+ E-HCOOH and (ii)OCO® mechanisms, i.e., *+CO2+ H+ E-OCO+ H+ E-HCOOH, corresponding to two different intermediates, *CoOH and *OCHO.
As can be seen in Figure 5c, on Bi-Cu or Bi-O-Cu, *CoOH production is more endothermic than *OCO, and therefore the *OHo mechanism is more feasible for HCOOH formation, which is consistent with other reported results. In addition, by comparing the energy distribution of the *OCO mechanism on the Bi-Cu and Bi-O-Cu, we can find that on the Bi-Cu, the *OCO hydrogenation (*OCO + H+ E-HCOOH) rate -*HCOOH formation limiting step, corresponding to 0Big Gibbs free energy change at 58 ev;In contrast, the rate-limiting step (*CO2+ H+ E-ocho + H+ E-) formed by *OChe is easier on the Bi-O-Cu, which only absorbs 027EV intermediate *ocho than bi-cu.
In general, Bi-O-Cu is more conducive to HCOOH formation due to the weak adsorption of *OCHO.
yuanwei liu, zhen xin lou, xuefeng wu, bingbao mei, jiacheng chen, jia yue zhao, ji li, hai yang yuan, *zhu, sheng dai, chenghua sun, peng fei liu, zheng jiang, hua gui yang. molecularly distorted local structure in bi2cuo4 oxide to stabilize lattice oxygen for efficient formate electrosynthesis. adv. mater. 2022.