Density Functional Theory Mechanistic Study on H₂O₂ Production Using an Organic Semiconductor Epindolidione

Abstract

Organic semiconductors have recently emerged as promising catalytic materials for oxygen reduction to hydrogen peroxide, H 2 O 2 , a chemical of great importance in industry as well as biology. While examples of organic semiconductor-mediated photocatalytic and electrocatalytic processes for H 2 O 2 production become more numerous and improve in performance, fundamental understanding of the reaction mechanisms at play have been explored far less. The aim of the present work is to computationally test hypotheses of how selective oxygen reduction to H 2 O 2 generally occurs on carbonyl dyes and pigments. As an example material, we consider epindolidione (EPI), an industrial pigment with demonstrated semiconductor properties, which photocatalytic activity in oxygen reduction reaction (ORR) and thereby producing hydrogen peroxide (H 2 O 2 ) in low pH environment has been recently experimentally demonstrated. In this work, the ability of the reduced form of EPI, viz. EPI-2H (which was formed after a photoinduced 2e − /2H + process), to reduce molecular triplet oxygen to peroxide and the possible mechanism of this reaction are computationally investigated using density functional theory. In the main reaction pathway, the reduction of O 2 to H 2 O 2 reaction occurs via abstraction of one of the hydrogen atoms of EPI-2H by triplet dioxygen to produce an intermediate complex consisting of the radicals of hydrogen peroxide (HOO • ) and EPI-H • at the initial stage. HOO • thus released can abstract another hydrogen atom from EPI-H • to produce H 2 O 2 and regenerates EPI; otherwise, it can enter another pathway to abstract hydrogen from a neighboring EPI-2H to form EPI-H • and H 2 O 2 . EPI, after reduction, thus plays in ORR the role of hydrogen atom transfer (HAT) agent via its OH group, similar to anthraquinone in the industrial process, while HAT from its amino hydrogen is found unfavorable.

Faradaic Pixels for Precise Hydrogen Peroxide Delivery to Control M‐Type Voltage‐Gated Potassium Channels

“…Several organic small‐molecules as well as polymers have shown the ability to photo(electro)catalytically reduce oxygen to peroxide and/or superoxide. [ 52 , 53 ] Published results for using PEDOT as an electrocatalyst for peroxide evolution demonstrated stable operation for at least 24 h of galvanostatic current. [ 39 ] In line with this, we repeatedly tested the PEDOT‐based faradaic pixels and did not observe any degradation or drop in performance.…”

Polymerized Riboflavin and Anthraquinone Derivatives for Oxygen Reduction Reaction

“…Similarly structured electrocatalysts such as quinacridone and epindolidione offer similar efficiencies as pRF of 96%, however, these studies were performed in highly acidic media. [33,83] Further product quantification has been performed on perylene tetracarbonyl imide, which offers structural similarities to anthraquinones. Here, an efficiency of 70% was reached, which was rapidly degrading throughout the electrolysis.…”

Recent Advancement in Piezopolarization Induced Photocatalytic H2O2 Production: Fundamentals, Theoretical Insights, and Future Endeavors

“…In this context, robust computational tools such as DFT have significant potential for comprehending the basic properties of materials and verifying the underlying mechanisms of piezophototronic-induced catalysis, including relevant parameters like work function and band positions, at a fundamental level. In addition to conventional DFT, which is confined to limited atom count, high-throughput DFT, capable of handling thousands of atoms within a material, stands out as a practical and advanced tool for exploring new computational technologies. − …”