Cobalt-Loaded Carbon Nitride Demonstrates Enhanced Photocatalytic Production of H2 from Lignocellulosic Biomass Components.

Abstract

Photocatalytic production of hydrogen (H₂) from biomass is a promising avenue for advancing sustainable energy generation. We prepared carbon nitride (CN _x ) with cobalt (Co) as an oxidation cocatalyst (denoted CN _x /Co) to improve photocatalytic H₂ production through photoreforming components of lignocellulosic biomass under visual light irradiation. CN _x /Co was synthesized by loading Co onto preformed CN _x through a straightforward thermal deposition. The thermal loading of Co at 450 °C led to the formation of a mixed valence CoO _x , which shifted Co²⁺ character to Co³⁺ over the course of the hydrogen evolution reaction (HER). Compared to CN _x without Co, our materials with 0.3 and 0.6 wt % Co demonstrate twice the apparent quantum yield (AQY) for H₂ production under irradiation at 405 nm using glucose as a sacrificial electron donor (3.0% and 2.8%, respectively, vs 1.4%). Time-resolved spectroscopic investigations indicate that the Co extracts charges in the subnanosecond time scale and promotes the formation of beneficial long-lived charges. Impressively, some photocatalytic activity is observed when using the robust polymers of cellulose and lignin as the oxidation substrates (0.2 and 0.1% AQY, respectively). The ability to oxidize abundant biomass without extensive prepreparation is promising for waste upcycling applications.