Oxidation State Modulation of Bimetallic Tin-Copper Oxide Nanotubes for Selective CO₂ Electroreduction to Formate

In this work, the oxidation state of Sn and Cu active sites for CO₂ electroreduction via constructing a Sn-Cun bimetallic oxide composite with a nanotube structure (SnCu-CNS) is successfully modulated. Compared to a single SnO₂ or CuO_x component, the SnCu-CNS composite holds reinforced electronegativity to generate unique extra Sn^δ+ centers and higher CuO centers with enhanced oxidation effect. Based on density functional theory calculations, the enlarged energy difference between Sn^δ+ /CuO centers and the reactants accelerates the electron transfer and decreases the energy barrier for the key intermediates to gain higher formate selectivity. Furthermore, the hollow structure and abundant micropores of SnCu-CNS are also conducive to the reactant transport and availability of active sites during CO₂ electroreduction. In a conventional H-type cell, SnCu-CNS catalyst exhibits a maximum 95.1% faradaic efficiency for formate production. Switching to a flow cell configuration, SnCu-CNS can further deliver partial current densities exceeding 200 mA cm^-2 and over 90% faradaic efficiencies for the formate, superior to most of the reported Sn-based electrocatalysts. This strategy of electronic modulation and morphology engineering in bimetallic oxides can have wide applications to raise electrocatalytic performance.