The role of electrolyte acid concentration in the electrochemical exfoliation of graphite:Mechanism and synthesis of electrochemical graphene oxide

Electrochemistry has emerged as a major route for graphene and graphene oxide synthesis from graphite.Anodic graphite oxidation is commonly used with dilute mineral acid or aqueous salt electrolytes.In this system,the electrolyte acid concentration appears to be a critical parameter.However,the effect of the acid concentration,particularly at low concentrations,is still not fully understood.To address this issue,we used a packed bed electrochemical reactor to synthesize seven different electrochemical graphite oxide(EGO)products in 2–16M sulfuric acid.Detailed XRD,XPS,Raman,conductivity and optical microscopy analysis of the products was carried out.We found dilute acid(<10 M)graphite oxides were less crystalline and less oxidized than those produced in stronger acids.The oxygen evolution reaction at the graphite surface appears to affect the structural changes,oxidation mechanism,and electrochemical corrosion of the anode.EGO conductivity is also strongly affected by the electrolyte’s acidity.We show that well oxidized,yet reasonably conductive,single layer graphene oxide can be produced from 7.1M acid.These results broaden our understanding of graphite electrochemistry and will serve to inform future electrochemical graphene synthesis efforts.

Operando reconstruction-induced CO_(2)reduction activity and selectivity for cobalt-based photocatalysis

The oxygen atom coordination inducing the structure reconstruction of the catalytic site is identified and recognized ambiguously,which is related to accurately declare the mechanism in a dynamic catalytic process.Herein,we demonstrated that the reconstructed catalytic sites would lead to a remarkable performance for photocatalytic CO_(2)reduction.At the initial 4-cycles testing,the in-situ formation of CoOx active sites on the Co(CoP)surface performed an increasing transient activity and selectivity toward CO evolution.The formation of reconstructive Co-O bond and the appearance of intermediate specie CO were simultaneously observed by the pre-operando Raman,revealing the dynamic relationship between catalytic site structure and the photocatalytic properties.Moreover,density functional theory calculations showed that the electronic structure of the reconstructive surface sites could modulate the ability of CO_(2)adsorption and CO desorption.The reduced barrier energy for the rate-determining step finally improved the activity and selectivity of CO_(2)reduction.

Highly active CeO_2 hollow-shell spheres with Al doping

Metal oxide hollow structures are of great inter- est in many current and emerging areas of technology. This paper presents a facile and controlled protocol for the syn- thesis of Al-doped CeO2 hollow-shell spheres （CHS）, where the dopant confers enhanced stability and activity to the ma- terial. These Al-doped CeO2 hollow-shell spheres （ACHS） possess a controllable shell number of up to three, where the sizes of the exterior, middle, and interior spheres were about 250-100 nm,150-50 nm, and 40-10 nm, respectively, and the average shell thickness was -15 nm. The thermal stability of the ACHS structure was enhanced by the homogeneous in- corporation of AI atoms, and more active oxygen species were present compared with those in the non-doped congener. Au NPs supported on ACHS （Au/ACHS） showed superior cat- alytic performance for the reduction of p-nitrophenol. For the same Au NP content, the reaction rate constant （k） of the Au/ACHS was nearly twice that of the non-doped Au/CHS, indicating that AI doping is promising for improving the per- formance of inert or unstable oxides as catalyst supports.

Ru(bpy)_(3)^(2+)-sensitized{001}facets LiCoO_(2) nanosheets catalyzed CO_(2) reduction reaction with 100% carbonaceous products

Photosensitized heterogeneous CO_(2) reduction(PHCR)has emerged as a promising means to convert CO_(2) into valuable chemicals,however,challenged by the relatively low carbonaceous product selectivity caused by the competing hydrogen evolution reaction(HER).Here,we report a PHCR system that couples Ru(bpy)32+photosensitizer with{001}faceted LiCoO_(2) nanosheets photocatalyst to simultaneously yield 21.2 and 722μmol·g^(-1)·h^(-1) of CO,and 4.42 and 108μmol·g^(-1)·h^(-1) of CH4 under the visible light and the simulated sunlight irradiations,respectively,with completely suppressed HER.The experimental and theoretical studies reveal that the favored CO_(2) adsorption on the exposed Li sites on{001}faceted LiCoO_(2) surface is responsible for the completely suppressed HER.