Engineering Facets and Oxygen Vacancies over Hematite Single Crystal for Intensified Electrocatalytic H₂O₂ Production

Abstract

Hydrogen peroxide is a highly valuable chemical, and electrocatalytic oxygen reduction towards H2O2 offers an alternative method for safe on‐site applications. Generally, low‐cost hematite (α‐Fe2O3) is not recognized as an efficient electrocatalyst because of its inert nature, but it is herein reported that α‐Fe2O3 can be endowed with high catalytic activity and selectivity via the engineering of facets and oxygen vacancies. Density‐functional theory (DFT)calculations predict that the {001} facet is intrinsically selective for H2O2 production, and that oxygen vacancies can trigger the high activity, providing sites for O2 adsorption and protonation, stabilizing the *OOH intermediate, and preventing cleavage of the OO bond. The synthesized oxygen‐defective α‐Fe2O3 single crystals with exposed {001} facets achieve high selectivities for H2O2 of >90%, >88%, and >95% in weakly acidic, neutral, and alkaline electrolytes, respectively, and the H2O2 production rate reaches 454 mmol g−1cat h−1 at 0.1 V versus RHE under alkaline conditions. In an anion exchange membrane fuel cell, a maximum H2O2 production of 546.8 mmol L−1 with a high Faradaic efficiency of 80.5% is achieved. Thus, this work details a low‐cost catalyst feasible for H2O2 synthesis, and highlights the feasibility of theoretical catalyst design for practical applications.

High‐Efficiency Electrosynthesis of Hydrogen Peroxide from Oxygen Reduction Enabled by a Tungsten Single Atom Catalyst with Unique Terdentate N1O2 Coordination

“…[ 8,9 ] Recently, the direct reaction of gaseous H 2 and O 2 driven by thermocatalysis is considered as another feasible approach for the synthesis of H 2 O 2 , but such thermal catalytic route suffers from safety and productivity issues. [ 10,11 ] Therefore, a cost‐effective and environment‐friendly alternative technique is still required to realize green H 2 O 2 synthesis. Electrochemical oxygen reduction reaction (ORR) through a selective two‐electron (2e – ) pathway (acidic condition: O 2 + 2H + + 2e – → H 2 O 2 or alkaline condition: O 2 + H 2 O + 2e – → HO 2 – + OH – ) represents a promising method to generate H 2 O 2 due to some notable advantages of renewable energy source, mild reaction conditions and green on‐site production.…”

Selenium-Rich Configuration and Amorphization for Synergistically Maximizing the Active-Center Amount of CoSe1+x Nanodots toward Efficient Photocatalytic H2 Evolution

“…Sustainable H 2 production by photocatalysis is a green and environmentally friendly candidate to meet the global energy shortage. − However, single photocatalysts still suffers from serious recombination of photogenerated charges, which severely impedes further practical applications. − To solve the above problems and realize efficient photocatalytic activity, different strategies have been explored involving construction of a heterojunction, , cocatalyst modification, , and morphology engineering. , Among them, integrating cocatalysts has been proven to be a versatile means to dramatically boost the photocatalytic activity, which not only can expedite the separation of photoexcited carriers but also minimize the activation energy of H 2 production. − Particularly, platinum group metals have been widely used to enhance the activity of various photocatalytic materials (including TiO 2 , CdS, and g-C 3 N 4 ), , but their exorbitant price and low abundance seriously limit the commercialization process. − Therefore, it is very essential to further explore cheap and highly active hydrogen generation cocatalysts for signally improving the efficiency of water splitting. − …”

Identification of the Evolving Dynamics of Coordination-Unsaturated Iron Atomic Active Sites under Reaction Conditions

“…19 The key to endowing single-site irons with efficient ORR performance is reducing the d electrons participating in the reduction reaction to accelerate O 2 adsorption and O−O cleavage dynamics. 20 Theoretically, as the coordination number of the single-atom site decreases and approaches a near-free state, which is accompanied by fewer d electrons, binding with the reactants is more energetic and achieves the desired electron-reduction reaction. 21,22 Recently, covalent organic frameworks (COFs) with strong covalent bonds possess robust skeleton structure and surface amino groups with electronegative surfaces and can be used as metal anchors.…”

“…Single-atom catalysts (SACs) with uniform distribution of catalytic active sites possess an adjustable porous structure and an accessible metal active center, which are widely used in catalytic reactions. , Unfortunately, most single-site iron atoms which are supported and highly coordinated with electronegative elements (such as C, N, S) are inactive in O 2 reduction to H 2 O/OH – because of the sluggish O 2 adsorption and O–O cleavage . The key to endowing single-site irons with efficient ORR performance is reducing the d electrons participating in the reduction reaction to accelerate O 2 adsorption and O–O cleavage dynamics . Theoretically, as the coordination number of the single-atom site decreases and approaches a near-free state, which is accompanied by fewer d electrons, binding with the reactants is more energetic and achieves the desired electron-reduction reaction. , Recently, covalent organic frameworks (COFs) with strong covalent bonds possess robust skeleton structure and surface amino groups with electronegative surfaces and can be used as metal anchors. , Importantly, the amino-derived M–N bond has a weak force constant and is expected to be broken under the voltage-driven condition during the reaction to form a coordination-unsaturated metal center, which accelerates the adsorption of O 2 and O–O bonds cleavage dynamics.…”