Ultrasmall CoP Nanoparticles as Efficient Cocatalysts for Photocatalytic Formic Acid Dehydrogenation

Abstract

Photocatalytic dehydrogenation of formic acid (FA) under mild conditions can meet the increasing demand for H2 generation in a sustainable manner. In this work, ultrasmall CoP nanoparticle (NP) is first introduced as an efficient and robust cocatalyst for photocatalytic FA dehydrogenation. Both the density function theory and experimental results show excellent H2 production property for CoP NPs. The H2 production rate for the CdS/CoP@RGO hybrid under visible light irradiation without any additives can reach up to 182 ± 12.5 μmol·mg−1·hr−1, which is more than 30 times higher than that of bare CdS and over 3 times the reported value of classical noble metal Pd/C3N4 photocatalysts. The system can be sustained for more than 7 days, which is promising for practical application. The present work not only introduces a highly active catalyst but also provides a feasible strategy for construction of a low-cost photocatalytic FA dehydrogenation system under mild conditions. Formic acid (FA), which holds the merits of low cost, low toxicity, high stability, and high gravimetric hydrogen content, is considered a promising hydrogen carrier. Hydrogen can be released from FA in the presence of suitable catalysts via dehydrogenation (HCOOH → H2 + CO2, ΔG0 = −48.8 kJ·mol−1) with carbon dioxide as the only byproduct. Considering the environment and energy problem and the various merits of solar energy, exploring low-cost and acid-resistant FA dehydrogenation photocatalysts with enhanced activity and stability is urgent. In this work, the novel cobalt phosphide (CoP) nanoparticle, composed of earth-abundant elements, is introduced as a spectacular catalyst in photocatalytic FA dehydrogenation, with H2 production efficiency that could exceed that of the noble metals. Moreover, the system does not require elevated temperature to reach robust catalytic efficiency, which is greatly beneficial to its widespread application. Ultrasmall CoP nanoparticle (NP) is successfully synthesized and first introduced as an efficient and robust cocatalyst for photocatalytic FA dehydrogenation. The H2 production rate can reach up to 182 ± 12.5 μmol·mg−1·hr−1 and exceed the classical noble-metal catalysts. The system also has excellent selectivity (>99.5%) and stability (>7 days). DFT simulation and experimental results indicate that CoP needs lower H2 desorption energy compared with noble-metal Pt in the H2 production process.