A phosphate-derived bismuth catalyst with abundant grain boundaries for efficient reduction of CO2 to HCOOH.

Electroreduction of CO2 to HCOOH with high current densities and efficiencies remains a challenge. Herein, we developed a metallic Bi catalyst with abundant grain boundaries through the electrochemical transformation of BiPO4 nanorods to boost the catalytic performance of the electroreduction of CO2 to HCOOH. The phosphate-derived Bi catalyst (PD-Bi) achieved an FE of 91.9% for HCOOH at a high current density of -600.0 mA cm-2. Mechanistic study revealed that the abundant grain boundaries within PD-Bi promoted the adsorption of CO2 and stabilization of the CO2˙- intermediate, resulting in facilitated CO2 activation and thus enhanced catalytic performance.

Bi@Sn Core-Shell Structure with Compressive Strain Boosts the Electroreduction of CO2 into Formic Acid.

As a profitable product from CO2 electroreduction, HCOOH holds economic viability only when the selectivity is higher than 90% with current density (j) over -200.0 mA cm-2. Herein, Bi@Sn core-shell nanoparticles (Bi core and Sn shell, denoted as Bi@Sn NPs) are developed to boost the activity and selectivity of CO2 electroreduction into HCOOH. In an H-cell system with 0.5 m KHCO3 as electrolyte, Bi@Sn NPs exhibit a Faradaic efficiency for HCOOH (FEHCOOH) of 91% with partial j for HCOOH (j HCOOH) of -31.0 mA cm-2 at -1.1 V versus reversible hydrogen electrode. The potential application of Bi@Sn NPs is testified via chronopotentiometric measurements in the flow-cell system with 2.0 m KHCO3 electrolyte. Under this circumstance, Bi@Sn NPs achieve an FEHCOOH of 92% with an energy efficiency of 56% at steady-state j of -250.0 mA cm-2. Theoretical studies indicate that the energy barrier of the potential-limiting step for the formation of HCOOH is decreased owing to the compressive strain in the Sn shell, resulting in the enhanced catalytic performance.