P-Block Aluminum Single-Atom Catalyst for Electrocatalytic CO₂ Reduction with High Intrinsic Activity

Abstract

Atomically dispersed transition metal sites on nitrogen-doped carbon catalysts hold great potential for the electrochemical CO₂ reduction reaction (CO₂RR) to CO due to their encouraging selectivity. However, their intrinsic activity is restricted by the hurdle of the high energy barrier of either *COOH formation or *CO desorption due to the scaling relationship. Herein, we discover a p-block aluminum single-atom catalyst (Al-NC) featuring an Al-N₄ site that enables disentangling this hurdle, which endows a moderate reaction kinetic barrier for *COOH formation and *CO desorption, as validated by in situ attenuated total reflection infrared spectroscopy and theoretical simulations. As a result, the developed Al-NC shows a CO Faradaic efficiency (FE_CO) of up to 98.76% at -0.65 V vs RHE and an intrinsic catalytic turnover frequency of 3.60 s^-1 at -0.99 V vs RHE, exceeding those of the state-of-the-art Ni-NC and Fe-NC counterparts. Moreover, it also delivers a partial CO current of 309 mA·cm^-2 at 93.65% FE_CO and 605 mA at >85% FE_CO in a flow cell and membrane electrode assembly (MEA), respectively. Strikingly, when using low-concentration CO₂ (30%) as the feedstock, this catalyst can still deliver a partial CO current of 240 mA at >80% FE_CO in the MEA. Considering the earth-abundant character of the Al element and the high intrinsic activity of the Al-NC catalyst, it is a promising alternative to today's transition metal-based single-atom catalysts.