One-Step Phase Separation for Core-Shell Carbon@Indium Oxide@Bismuth Microspheres with Enhanced Activity for CO2 Electroreduction to Formate.

It is a substantial challenge to construct electrocatalysts with high activity, good selectivity, and long-term stability for electrocatalytic reduction of carbon dioxide to formic acid. Herein, bismuth and indium species are innovatively integrated into a uniform heterogeneous spherical structure by a neoteric quasi-microemulsion method, and a novel C@In2 O3 @Bi50 core-shell structure is constructed through a subsequent one-step phase separation strategy due to melting point difference and Kirkendall effect with the nano-limiting effect of the carbon structure. This core-shell C@In2 O3 @Bi50 catalyst can selectively reduce CO2 to formate with high selectivity (≈90% faradaic efficiency), large partial current density (24.53 mA cm-2 at -1.36 V), and long-term stability (up to 14.5 h), superior to most of the Bi-based catalysts. The hybrid Bi/In2 O3 interfaces of core-shell C@In2 O3 @Bi will stabilize the key intermediate HCOO* and suppress CO poisoning, benefiting the CO2 RR selectivity and stability, while the internal cavity of core-shell structure will improve the reaction kinetics because of the large specific surface area and the enhancement of ion shuttle and electron transfer. Furthermore, the nano-limited domain effect of outmost carbon prevent active components from oxidation and agglomeration, helpful for stabilizing the catalyst. This work offers valuable insights into core-shell structure engineering to promote practical CO2 conversion technology.

In-situ generation of In2O3 nanoparticles inside In[Co(CN)6] quasi-metal-organic-framework nanocubes for efficient electroreduction of CO2 to formate.

Three-dimensional (3D) network structure of metal-organic framework (MOF) can accommodate outstanding electrocatalysis performances, but always collapse during the conversion to active materials or applications process. How to maintain the 3D network when producing active species is of great importance for full application of MOF. Herein, a new MOF material, In[Co(CN)6] (In-Co PBA) nanocubes, are firstly synthesized. Through a controlled low-temperature deligandation process, the In-Co PBA nanocubes are transformed to a novel In2O3@In-Co PBA quasi-MOF nanocubes, which basically retain the 3D porous structure of PBA but with in situ generated In2O3 nanoparticles inside. When used as CO2RR electrocatalyst, such a novel cubic composite structure exhibits excellent performances with faradaic efficiency of 85% for formate at a potential of -0.96 V and with current density of 31.5 mA·cm-2 at -1.32 V, surpassing most of the reported indium-based catalysts. The excellent performance can be attributed to the special composite structure, which provides not only active sites by In2O3 nanoparticles to catalyze CO2RR, but also the 3D porous framework by quasi-MOF to accelerate gaseous exchange and electrolyte permeation and prevent the electrode choking. This work offers a new strategy for the design of post-transition metal catalysts and the structure design of quasi-MOF.