Our understanding of the fundamental structure and bonding of graphene oxide (GO) as well as the scope of its utility have grown tremendously over the past decade. As a result, the pace of research efforts directed toward this carbon material continues to increase. Contemporary application now intersects a variety of disciplines and includes heterogeneous catalysis, flow reactor technologies, biomedicine and biotechnology, polymer composites, energy storage, and chemical sensors. Advances in these areas have been buoyed by improvements in the methods used to synthesize and characterize GO, as well as functionalized derivatives thereof. While the diverse uses of GO have been reviewed previously, herein we provide an overview of some of the most recent and significant developments in the field. A brief overview of GO's synthesis and characterization is also provided as well as several recently proposed structural models. The inherent reactivity of GO is described in the context of catalysis, and the utilization of GO's reactive oxygen groups and carbon framework to prepare functionalized derivatives is also discussed. Finally, we provide an outlook of potential areas where GO, its derivatives, and related materials may be expected to find utility or opportunity for further growth and study.

Harnessing the chemistry of graphene oxide

Nanocomposite TiO2/graphene photocatalysts were synthesized via solvothermal process using titanium isopropoxide as a TiO2 precursor. Surfactant-stabilized graphene (ssG) prepared via liquid phase exfoliation and graphene oxide (GO) obtained via oxidation of graphite were used for preparation of two types of composites TiO2/G and TiO2/rGO, respectively, each with graphene loadings 0.01%, 0.1% and 1%. Hydrophilic non ionic surfactant Pluronic F127 was employed in order graphene stabilization in water and homogeneous dispersion with the TiO2 precursor to be achieved.

The crystalline structure, composition, morphology, porosity and light absorption of the photocatalysts and their photocatalytic activity in NOx oxidation under UV and visible light irradiation were comparatively investigated. The titania/graphene (ssG and rGO) nanocomposites exhibited higher photocatalytic efficiency than pure TiO2 especially under visible light irradiation in terms of total NOx (NO and NO2) removal and NO2 emission. Differences in the photocatalytic efficiency between the TiO2/G and TiO2/rGO composites were observed originating from the type and the loading of the graphene. In general, the TiO2/rGO exhibited superior efficiency than the TiO2/G and the best results were recorded for low 0.1% graphene loading. The findings are discussed taking into consideration the variation in the BET SSA and the Eg values, as well as the differences in the electronic structure of the ssG and the rGO, the former to be a zero-band gap material and the latter a semiconductor with tunable band gap. The presence of graphene component was determined as a key parameter governing the separation of the photogenerated electron–holes pair through interfacial charge transfer. The significantly increased activity of the TiO2/rGO composites under visible light in NOx removal and the very low levels of NO2 release in comparison to the pure TiO2 render these materials promising photocatalysts for efficient air purification.

TiO2/graphene composite photocatalysts for NOx removal: A comparison of surfactant-stabilized graphene and reduced graphene oxide

Effect of hydrogen peroxide on properties of graphene oxide in Hummers method

Seawater electrolysis is an extremely attractive approach for harvesting clean hydrogen energy, but detrimental chlorine species (i.e., chloride and hypochlorite) cause severe corrosion at the anode. Here, we report our recent finding that benzoate anions-intercalated NiFe-layered double hydroxide nanosheet on carbon cloth (BZ-NiFe-LDH/CC) behaves as a highly efficient and durable monolithic catalyst for alkaline seawater oxidation, affords enlarged interlayer spacing of LDH, inhibits chlorine (electro)chemistry, and alleviates local pH drop of the electrode. It only needs an overpotential of 320 mV to reach a current density of 500 mA·cm–2 in 1 M KOH. In contrast to the fast activity decay of NiFe-LDH/CC counterpart during long-term electrolysis, BZ-NiFe-LDH/CC achieves stable 100-h electrolysis at an industrial-level current density of 500 mA·cm–2 in alkaline seawater. Operando Raman spectroscopy studies further identify structural changes of disordered δ (NiIII-O) during the seawater oxidation process.

https://www.sciopen.com/article_pdf/1557931195381764097.pdf

Benzoate anions-intercalated NiFe-layered double hydroxide nanosheet array with enhanced stability for electrochemical seawater oxidation

Ni-Graphene oxide (GO) composite coatings were electrodeposited over mild steel substrate. The coatings exhibited compact and crack free morphology. Incorporation of GO facilitated grain growth along low energy (111) and (200) atomic planes without any significant alteration in the crystallite size. Compositional analysis suggested uniform distribution of GO within the coating for lower GO concentration. Whereas for higher GO concentrations, agglomeration and non-uniform distribution of GO within the coating microstructure was noticed. Corrosion behaviour of coatings was studied by electrochemical impedance spectroscopy and potentiodynamic polarisation techniques. It was observed that the corrosion rate of the coating initially decreased with the addition of GO. After an optimum GO concentration which produced the lowest corrosion rate, further addition of GO resulted in increase in the corrosion rate. The initial decrease in the corrosion rate was attributed to the coating growth along the low energy low index planes and the impermeability of the GO to the electroactive media. The increase in the corrosion rate beyond the optimum was attributed to the GO agglomeration which caused inhomogeneous distribution of GO in the coating and relatively non-uniform coating morphology.

Ni-graphene oxide composite coatings: Optimum graphene oxide for enhanced corrosion resistance

The rational construction of earth‐abundant and advanced electrocatalysts for oxygen evolution reaction (OER) is extremely desired and significant to seawater electrolysis. Herein, by directly etching Ni3S2 nanosheets through potassium ferricyanide, a novel self‐sacrificing template strategy is proposed to realize the in situ growth of NiFe‐based Prussian blue analogs (NiFe PBA) on Ni3S2 in an interfacial redox reaction. The well‐designed Ni3S2@NiFe PBA composite as precursor displays a unique spherical magic cube architecture composed of nanocubes, which even maintains after a phosphating treatment to obtain the derived Ni3S2/Fe‐NiPx on nickel foam. Specifically, in alkaline seawater, the Ni3S2/Fe‐NiPx as OER precatalyst marvelously realizes the ultralow overpotentials of 336 and 351 mV at large current densities of 500 and 1000 mA cm–2, respectively, with remarkable durability for over 225 h, outperforming most reported advanced OER electrocatalysts. Experimentally, a series of characterization results confirm the reconstruction behavior in the Ni3S2/Fe‐NiPx surface, leading to the in situ formation of Ni(OH)2/Ni(Fe)OOH with abundant oxygen vacancies and grain boundaries, which constructs the Ni3S2/Fe‐NiPx reconstruction system responsible for the remarkable OER catalytic activity. Theoretical calculation results further verify the enhanced OER activity for Ni3S2/Fe‐NiPx reconstruction system, and unveil that the Fe‐Ni2P/FeOOH as active origin contributes to the central OER activity.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/advs.202104846

Spherical Ni3S2/Fe‐NiP x Magic Cube with Ultrahigh Water/Seawater Oxidation Efficiency

X-ray diffraction patterns of graphite oxide (GO) are theoretically simulated as a function of the displacements of carbon atoms using the Debye—Waller factor in terms of the Warren—Bodenstein equation. The results demonstrate that GO has the turbostratically stacked structure. The high order (00l) peaks gradually disappear with the increase in atomic thermal vibrations along c-axis while the (hk0) ones weaken for the vibrations along a-axis. When the displacement deviation ua = 0.015 nm and uc = 0.100 nm the computed result is consistent with the experimental measurements.

https://iopscience.iop.org/article/10.1088/0256-307X/30/9/096101/pdf

X-Ray Difraction Pattern of Graphite Oxide

Single‐atom catalysts, featuring some of the most unique activities, selectivity, and high metal utilization, have been extensively studied over the past decade. Given their high activity, selectivity, especially towards small molecules or key intermediate conversions, they can be synergized together with other active species (typically other single atoms, atomic clusters, or nanoparticles) in either tandem or parallel or both, leading to much better performance in complex catalytic processes. Although there have been reports on effectively combining the multiple components into one single catalytic entity, the combination and synergy between single atoms and other active species have not been reviewed and examined in a systematic manner. Herein, in this overview, the key synergistic interactions, binary complementary effects, and the bifunctional functions of single atoms with other active species are defined and discussed in detail. The integration functions of their marriages are investigated with particular emphasis on the homogeneous and heterogeneous combinations, spatial distribution, synthetic strategies, and the thus‐derived outstanding catalytic performance, together with new light shined on the catalytic mechanisms by zooming in several case studies. The dynamic nature of each of the active species and in particular their interactions in such new catalytic entities in the heterogeneous electrocatalytic processes are visited, on the basis of the in situ/operando evidence. Last, we feature the current challenges and future perspectives of these integrated catalytic entities that can offer guidance for advanced catalyst design by the rational combination and synergy of binary or multiple active species.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/idm2.12011

Nurturing the marriages of single atoms with atomic clusters and nanoparticles for better heterogeneous electrocatalysis

Tuning active sites in catalyst design is the key to boosting the intrinsic activity of hydrogen evolution reaction (HER). Cationic Ni has been widely established as an active site in nickel sulfide due to the relatively low Gibbs free energy of hydrogen adsorption (ΔGH*). However, one of the big unsettled issues is whether S can be activated as a more active site than Ni in NiS2. Herein, the swapping of catalytic active sites from cationic Ni to anionic S in a hierarchical structure consisting of NiS2 nanoflowers grown on dual‐phased NiS2‐NiS foam (denoted as NiS2/NiS2‐NiS) is shown. A combined study of theoretical calculations and X‐ray photoelectron spectroscopy analysis demonstrate the remarkably antidromic electron transfer from Ni to S sites, therefore relieving the adsorption of hydrogen species and endowing a higher intrinsic activity at the S site over the Ni site. The new catalyst therefore exhibits superior HER performance, identified by doubling in the intrinsic activity and a twofold increased turnover frequency value compared to its pure NiS2 counterpart (0.028 s−1 vs 0.015 s−1 at the applied overpotential of 200 mV). The NiS2/NiS2‐NiS electrode also demonstrates outstanding activity toward the oxygen evolution reaction and overall water splitting.

Swapping Catalytic Active Sites from Cationic Ni to Anionic S in Nickel Sulfide Enables More Efficient Alkaline Hydrogen Generation

Platinum (Pt), as a commonly used electrocatalyst in direct methanol fuel cells (DMFCs), suffers from sluggish kinetics of both the methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). Geometric engineering has been proven effective for improving the MOR and ORR activities. Thus, by modulating the Pt precursor and poly(vinylpyrrolidone) (PVP) dosages, different porous PtCu nanotubes constructed by hollow nanospheres, solid alloy, and Pt-rich skinned nanoparticles, respectively, are successfully synthesized. Among them, the solid PtCu alloy nanoparticle coherent nanotubes exhibit the specific activity 9.42 times higher than Pt/C toward MOR, while the hollow PtCu alloy nanosphere coherent nanotubes show the specific activity 4.85 times higher than Pt/C toward ORR. The different Pt:Cu ratios of hollow nanospheres, solid alloy, and Pt-rich skinned nanoparticles cause the differences in electron transfer from Cu to Pt as well as electronic structures of Pt. As a result, the binding energies of intermediates can be regulated, leading to the enhancement in MOR and ORR.

Shi-Jia Mu

Papers

Spherical Ni3S2/Fe‐NiP x Magic Cube with Ultrahigh Water/Seawater Oxidation Efficiency

X-Ray Difraction Pattern of Graphite Oxide

Nurturing the marriages of single atoms with atomic clusters and nanoparticles for better heterogeneous electrocatalysis

Swapping Catalytic Active Sites from Cationic Ni to Anionic S in Nickel Sulfide Enables More Efficient Alkaline Hydrogen Generation

Geometric Engineering of Porous PtCu Nanotubes with Ultrahigh Methanol Oxidation and Oxygen Reduction Capability.