Abstract
Direct CO reduction to formaldehyde (CORTF) provides an alternative, energy-efficient route for production of formaldehyde, a critical chemical commodity as well as promising hydrogen carrier. However, the conventional thermal catalysis approach is challenged with slow reaction kinetics, which can be attributed to imbalanced CO and hydrogen competitive chemisorption to catalyst, with stronger CO adsorption significantly inhibiting hydrogen adsorption that suppresses their reaction towards formaldehyde generation. We report a new, innovative CORTF mechanism to promote the reaction by utilizing hydrogen underpotential deposition to balance the species coverage on catalyst surface. Our study shows that, by separately tuning Pt alloy nanoparticle catalyst composition to control CO chemical adsorption favorability and tuning hydrogen underpotential deposition potential to control hydrogen electrochemical adsorption favorability, the formaldehyde production rate with Pt alloys (866 mg/gcat/h) is 300 times higher compared to conventional thermal catalysis method (2.6 mg/gcat/h) and 50 time higher than previously reported molybdenum phosphide (MoP, 16.3 mg/gcat/h) electrocatalyst. DFT simulations show reduced energy barriers for the rate-limiting steps by means of balancing hydrogen and CO adsorption, thus supporting this new mechanism to achieve more dramatically improved CORTF kinetics. This CORTF mechanism provides a new strategy towards efficient formaldehyde production.