Gold Nanocrystals and Conjugated Polymer-Wrapped Single-Walled Carbon Nanotube Composites for Catalyzing CO₂ Electroreduction

Metal nanocrystals (NCs) have been synthesized and used as highly efficient electrocatalysts for the electrocatalytic CO₂ reduction reaction (eCO₂RR) in recent years. Electrocatalysts with various metal sizes and morphologies have achieved remarkable improvement in the CO₂ reduction. However, the syntheses are typically energy-demanding and the catalysts exhibit low mass activity. Ultrasmall metal NCs synthesized by a one-step process at room temperature and an ambient environment stand out because of cost-effectiveness in materials and energy. Here, we report a facile synthesis to produce 1 nm gold nanocrystals in ambient conditions, which was realized by an in situ reduction of AuCl₃ on a semiconducting single-walled carbon nanotube (sc-SWCNT) surface. In addition, the bipyridine (BPy) units in tube-wrapped polymers function as chelating sites for anchoring Au3+ and AuNCs. The ultrasmall size of AuNCs was achieved by fast AuCl₃ diffusion and the anchoring function of BPy units. A slow diffusion or absence of BPy units resulted in AuNCs in larger sizes. The NC density was controlled by AuCl₃ feed amounts by varying the Au-to-BPy molar ratios. Density functional theory was applied to simulate the Au-BPy coordination. The fabricated nanocomposites exhibited a high Faradaic CO selectivity up to 86% at 25 mA/cm² and a high mass activity up to 5.61 A/mg (Au) at 100 mA/cm², which is the highest value reported so far in AuNC electrocatalysts for CO₂ reduction.