High‐Performance Overall CO 2 Splitting on Hierarchical Structured Cobalt Disulfide with Partially Removed Sulfur Edges

The ability to develop bifunctional electrocatalysts for concurrent CO 2 reduction reaction (CO 2 RR) and oxygen evolution reaction (OER) is the key to the practical application of CO 2 splitting to produce CO. However, this remains a grand challenge. Herein, a robust strategy to rationally craft hierarchical structured bifunctional electrocatalysts composed of 3D CoS 2 nanocages interconnected on 2D CoS 2 nanosheet arrays (denoted hierarchical CoS 2 nanocages) for high‐performance CO 2 splitting is developed. The subsequent calcination removes the partial S edges of CoS 2 , thereby strongly suppressing the hydrogen evolution reaction (HER) of CoS 2 . By combining theoretic and experimental results, for the first time, it is discovered that the plane S of CoS 2 , instead of S edges, are highly active for CO 2 RR but inactive for HER, rendering the plane S as ideal active sites for CO 2 RR. Intriguingly, the composition tuning via calcination and the presence of a hierarchical architecture confer hierarchical CoS 2 nanocages respective outstanding CO 2 RR and OER performance. Notably, the hierarchical CoS 2 nanocages can be exploited as bifunctional electrocatalysts for overall CO 2 splitting to yield the current density of 1 mA cm −2 at a small cell voltage of 1.92 V, much lower than the widely reported values (>2.5 V).