Mechanistic analysis of multiple processes controlling solar-driven H2O2 synthesis using engineered polymeric carbon nitride

Yubao Zhao,Beibei Xiao,Zhenchun Yang,Wonyong Choi,Chun Hu,Shibo Xi,Tengfeng Xie,Caozheng Diao,Jingyu Gao,Sheng Chen,Lina Li,Peng Zhang

doi:10.1038/s41467-021-24048-1

Abstract

Solar-driven hydrogen peroxide (H2O2) production presents unique merits of sustainability and environmental friendliness. Herein, efficient solar-driven H2O2 production through dioxygen reduction is achieved by employing polymeric carbon nitride framework with sodium cyanaminate moiety, affording a H2O2 production rate of 18.7 μmol h −1 mg−1 and an apparent quantum yield of 27.6% at 380 nm. The overall photocatalytic transformation process is systematically analyzed, and some previously unknown structural features and interactions are substantiated via experimental and theoretical methods. The structural features of cyanamino group and pyridinic nitrogen-coordinated soidum in the framework promote photon absorption, alter the energy landscape of the framework and improve charge separation efficiency, enhance surface adsorption of dioxygen, and create selective 2e− oxygen reduction reaction surface-active sites. Particularly, an electronic coupling interaction between O2 and surface, which boosts the population and prolongs the lifetime of the active shallow-trapped electrons, is experimentally substantiated.

Highlights

Solar-driven hydrogen peroxide (H2O2) production presents unique merits of sustainability and environmental friendliness
The resulting polymeric carbon nitride (PCN) was further treated with sodium thiocyanate (NaSCN) molten salt to tailor the conjugated electronic structure and the surface properties
Further condensation reaction occurs in the molten salt and leads to two favorable structural features: (1) improved polymerization degree and expanded conjugated electronic structure[37,38,39,40]; and (2) conversion of the amino group to the sodium cyanaminate moiety

Summary

Introduction

Solar-driven hydrogen peroxide (H2O2) production presents unique merits of sustainability and environmental friendliness. Polymeric carbon nitride (PCN) consisting of the organic framework has the advantage of easy structural optimization[21,22,23,24,25,26,27]; its surface dangling functional groups and the conjugated electronic structure can be facilely modified for efficient catalytic reactions This unique advantage can be maximized only if the structure–photocatalytic activity relationship is clearly understood and taken into account in designing the PCN structure and composition[28,29,30]. A comprehensive mechanistic understanding on how the specific structural features influence each step in the photocatalytic 2e− oxygen reduction reaction (ORR) is challenging and unexplored, while such information is critical for the rational design of a highly efficient solar-driven H2O2 production system. It leads to enhanced accumulation of surface charges, stronger interaction beween surface and dioxygen, and higher density of catalytic active sites for selective 2e− ORR

Methods

Results

Conclusion