Engineering active grain boundaries (GBs) in oxide-derived (OD) electrocatalysts is critical to improve the selectivity in CO₂ reduction reaction (CO₂RR), which is becoming an increasingly important pathway for renewable energy storage and usage. Different from traditional in situ electrochemical reduction under CO₂RR conditions, where some metal oxides are converted into active metallic phases but with decreased GB densities, here we introduce the Li electrochemical tuning (LiET) method to controllably reduce the oxide precursors into interconnected ultrasmall metal nanoparticles with enriched GBs.

By using ZnO as a case study,¹ we demonstrate that the LiET-Zn with freshly exposed GBs exhibits a CO₂-to-CO partial current of ∼23 mA cm^–2 at an overpotential of −948 mV, representing a 5-fold improvement from the OD-Zn with GBs eliminated during the in situ electro-reduction process. Another representative study is on Cu₂O,² we report the tuning of facet exposure on Cu foil through battery cycling which gives a 6-fold improvement in C₂₊ to C₁ product ratio as compared to polished Cu foil with a maxima C₂₊ Faradaic efficiency over 60 % and H₂ below 20 %. Detailed mechanism study is carried out using density functional theory calculations to shed light on the energetics of the initial C-C coupling steps, while dynamic catalyst surface structure evolution and relevant reactive intermediates are monitored by in situ spectroelectrochemical techniques including Raman scattering and surface enhanced IR spectroscopy.

References:

(1) Jiang, K., Wang, H., Cai, W.B. & Wang, H. ACS Nano 11, 6451-6458 (2017).

(2) Jiang, K., Sandberg, R.B., Akey, A.J., Liu, X., Bell, D.C., Nørskov, J.K., Chan, K. & Wang, H. Nat. Catal. in press (2018).