Product selectivity in multielectron electrocatalytic reactions is crucial to energy conversion efficiency and chemical production. However, a present practical drawback is the limited understanding of actual catalytic active sites. Here, using as a prototype single-atom catalysts (SACs) in acidic oxygen reduction reaction (ORR), we report the structure-property relationship of catalysts and show for the first time that molecular-level local structure, including first and second coordination spheres (CSs), rather than individual active atoms, synergistically determines the electrocatalytic response. ORR selectivity on Co-SACs can be tailored from a four-electron to a two-electron pathway by modifying first (N or/and O coordination) and second (C-O-C groups) CSs. Using combined theoretical predictions and experiments, including X-ray absorption fine structure analyses and in situ infrared spectroscopy, we confirm that the unique selectivity change originates from the structure-dependent shift of active sites from the center Co atom to the O-adjacent C atom. We show this optimizes the electronic structure and *OOH adsorption behavior on active sites to give the present "best" activity and selectivity of >95% for acidic H2O2 electrosynthesis.

Tailoring Acidic Oxygen Reduction Selectivity on Single-Atom Catalysts via Modification of First and Second Coordination Spheres.

Graphene oxide (GO) is useful and promising material for graphene based applications in electronic, optics, chemistry, energy storage and biology. At the beginning of graphene history GO was only a simple and cheap step for preparation of single and multilayer graphene films and bulk structures by reduction. The further studies revealed the substantial structure imperfection of graphene oxide derived materials due to the defects in initial graphite and incompletion of reducing process. However, the results of recent research demonstrated a great amount of unique chemical, optical and electronic properties of graphene oxide that allow regarding it as independent nanomaterial possessing a large area of applications. In general, it represents the ultra-large organic molecule containing 2D carbon mesh. Unlike conventional graphene it provides wide range of chemical methods for attachment of various functional groups to its surface for control optical transparency, electrical and thermal conductance. Recently developed methods for preparation of graphene oxide derivatives saturated by carboxyl groups open the new attractive application areas in green technologies including energy storage and utilizing nuclear wastes. The goal of the review is to summarize the results of recent studies of graphene oxide, derivatives and reveal the most promising directions to focus the efforts of researchers.

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Graphene Oxide and Derivatives: The Place in Graphene Family

Highly Selective Hydrogen Peroxide Electrosynthesis on Carbon: In Situ Interface Engineering with Surfactants

Electrochemical production of hydrogen peroxide (H2 O2 ) through two-electron (2 e- ) oxygen reduction reaction (ORR) is an on-site and clean route. Oxygen-doped carbon materials with high ORR activity and H2 O2 selectivity have been considered as the promising catalysts, however, there is still a lack of direct experimental evidence to identify true active sites at the complex carbon surface. Herein, we propose a chemical titration strategy to decipher the oxygen-doped carbon nanosheet (OCNS900 ) catalyst for 2 e- ORR. The OCNS900 exhibits outstanding 2 e- ORR performances with onset potential of 0.825 V (vs. RHE), mass activity of 14.5 A g-1 at 0.75 V (vs. RHE) and H2 O2 production rate of 770 mmol g-1  h-1 in flow cell, surpassing most reported carbon catalysts. Through selective chemical titration of C=O, C-OH, and COOH groups, we found that C=O species contributed to the most electrocatalytic activity and were the most active sites for 2 e- ORR, which were corroborated by theoretical calculations.

Chemical Identification of Catalytically Active Sites on Oxygen-doped Carbon Nanosheet to Decipher the High Activity for Electro-synthesis Hydrogen Peroxide

The surface properties of the electrode materials play a crucial role in determining the performance and efficiency of energy storage devices. Graphene oxide and nanostructures of 3d transition metal oxides were synthesized for construction of electrodes in supercapacitors, and the electronic structure and oxidation states were probed using near-edge X-ray absorption fine structure. Understanding the chemistry of graphene oxide would provide valuable insight into its reactivity and properties as the graphene oxide transformation to reduced-graphene oxide is a key step in the synthesis of the electrode materials. Polarized behavior of the synchrotron X-rays and the angular dependency of the near-edge X-ray absorption fine structures (NEXAFS) have been utilized to study the orientation of the σ and π bonds of the graphene oxide and graphene oxide–metal oxide nanocomposites. The core-level transitions of individual metal oxides and that of the graphene oxide nanocomposite showed that the interaction of graph...

https://pubs.acs.org/doi/pdf/10.1021/jp503941t

X-ray Absorption Study of Graphene Oxide and Transition Metal Oxide Nanocomposites.

Great focus has been directed towards double-layer capacitance and Faradic, redox reactions because of their long device lifetimes and their high power densities, respectively Our novel approach to combining these mechanisms in a tri-layered composite electrode promises to increase the energy densities of the device, without sacrificing the supercapacitance and the high power densities attributed with it Initial analysis of the interfacial interactions of graphene oxide (GO) and manganese oxide (MnO2) were promising This paper aims to further demonstrate the tri-layered composite by forming a layer of reduced graphene oxide (rGO) on MnO2 nanowires and cobalt oxide nanorods We have successfully created the first of a kind supercapacitor electrode material as a scalable device In this paper, in addition to analysis of the composite electrode, we present modifications to the traditional electrophoretic deposition process and optimizations to the thermal reduction of GO in order to create rGO surfaces on substrates that are normally difficult to adhere it to

Cristina Javier

Papers

X-ray Absorption Study of Graphene Oxide and Transition Metal Oxide Nanocomposites.

Phoretic Deposition of Graphene on Manganese-Cobalt Oxide Composites for Supercapacitor Electrodes