Electrochemical water splitting is promising for utilizing intermittent renewable energy. The sluggish kinetics of the oxygen evolution reaction (OER), however, is a bottleneck in obtaining high efficiency. Only a few OER electrocatalysts have been developed for the use in acidic media despite the importance of a proton exchange membrane (PEM) water electrolyzer. IrO 2 is the only material that is both active and stable for the OER in highly corrosive acidic conditions. Herein, a facile and scalable synthesis of ultrathin IrO 2 nanoneedles is reported with a diameter of 2 nm using a modified molten salt method. The activity and durability for the OER are significantly enhanced on the ultrathin IrO 2 nanoneedles, compared to conventional nanoparticles. The ultrathin nanoneedles are successfully introduced to a PEM electrolyzer single cell with the enhanced cell performance.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Water electrocatalytic splitting is considered as an ideal process for generating H2 without byproducts. However, in the water-splitting reaction, a high overpotential is needed to overcome the high-energy barrier due to the slow kinetics of the oxygen evolution reaction (OER). In this study, we selected the 5-hydroxymethylfurfural (HMF) oxidation reaction, which is thermodynamically favored, to replace the OER in the water-splitting process. We fabricated three-dimensional hybrid electrocatalytic electrodes via layer-by-layer (LbL) assembly for simultaneous HMF conversion and hydrogen evolution reaction (HER) to investigate the effect of the nanoarchitecture of the electrode on the electrocatalytic activity. Nanosized graphene oxide was used as a negatively charged building block for LbL assembly to immobilize the two electroactive components: positively charged Au and Pd nanoparticles (NPs). The internal architecture of the LbL-assembled multilayer electrodes could be precisely controlled and their electrocatalytic performance could be modified by changing the nanoarchitecture of the electrode, including the thickness and position of the metal NPs. Even with a composition of the identical constituent NPs, the electrodes exhibited highly tunable electrocatalytic performance depending on the reaction kinetics as well as a diffusion-controlled process due to the sequential HMF oxidation and the HER. Furthermore, a bifunctional two-electrode electrolyzer for both the anodic HMF oxidation and the cathodic HER, which had an optimized LbL-assembled electrode for each reaction, exhibited the best full-cell electrocatalytic activity.

As an emerging concept for the development of new materials with nanoscale features, nanoarchitectonics has received significant recent attention.A mongt he various approaches that have been developed in this area, the fixeddirection construction of functional materials, such as layered fabrication, offers ah elpful starting point to demonstrate the huge potentialo fn anoarchitectonics. In particular, the combination of nanoarchitectonics with layer-by-layer (LbL) assembly and al arge degree of freedomi nc omponent availability and technical applicability would offer significant benefits to the fabrication of functional materials. In this Minireview,r ecent progress in LbL assembly is briefly summarized. After introducing the basicso fL bL assembly,r ecent advances in LbL research are discussed, categorized according to physical, chemical, and biological innovations, along with the fabrication of hierarchical structures.E xamples of LbL assemblies with graphene oxide are also described to demonstrate the broad applicability of LbL assembly,e ven with afixed material.Scheme1.Outline of the nanoarchitectonics concept:afusion of nanotechnology and the other research fields, the harmonization of various actions, and the conversion of simple self-assemblyinto hierarchical structures.

Oxygen reduction reaction (ORR) is an important reaction in energy conversion systems such as fuel cells and metal-air batteries. Carbon nanomaterials doped with heteroatoms are highly attractive materials for use as electrocatalysts by virtue of their excellent electrocatalytic activity, high conductivity, and large surface area. This study reports the synthesis of highly efficient electrocatalysts based on heteroatom-doped graphene nanosheets prepared through covalent functionalization using various small organic molecules and a subsequent thermal treatment. A series of nitrogen-doped reduced graphene oxide (NRGOn) nanosheets exhibited varying degrees and configurations of nitrogen atoms within the graphitic framework depending on the type of precursors used. On the basis of the rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) experiments, NRGO3, with a high degree of pyridinic-N content, displayed the desired one-step, quasi-four-electron transfer pathway during ORR, similar to commercial Pt/C. We also demonstrated the potential of covalent functionalization of sulfur and boron-doped graphene nanosheets.

With its superior electrical, optical, thermal, and mechanical properties, graphene offers a versatile platform for fabricating innovative hybrid composite materials with diverse potential applications. The preparation of graphene-based composites, particularly as thin films with nanoscale precision, is highly important for fabricating electrodes for energy and electronic devices as well as for facilitating understanding of the interplay between each component within the composites. In this context, the layer-by-layer (LbL) assembly technique offers a simple and versatile process for the fabrication of highly ordered multilayer film structures from various types of materials in a controllable manner. This paper presents details of the preparation and functionalization of these materials and the techniques for the LbL assembly of different graphenebased nanocomposites using polymers and nanoparticles. We anticipate that the protocols presented in this paper will guide researchers in the reproducible assembly of various high-quality graphene-based nanocomposites for fundamental researches and for diverse potential applications.

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The synergistic interplay between surface negative charges and functional groups in the carbon dot establish a strong Li-ion affinity, resulting in homogeneous Li deposition.

Controlling the architecture of hybrid nanomaterial electrodes is critical for understanding their fundamental electrochemical mechanisms and applying these materials in future energy conversion and storage systems. Herein, we report highly tunable electrocatalytic multilayer electrodes, composed of palladium nanoparticles (Pd NPs) supported by graphene sheets of varying lateral sizes, employing a versatile layer-by-layer (LbL) assembly method. We demonstrate that the electrocatalytic activity is highly tunable through the control of the diffusion and electron pathways within the 3-dimensional multilayer electrodes. A larger-sized-graphene-supported electrode exhibited its maximum performance with a thinner film, due to facile charge transfer by the mass transfer limited in the early stage, while a smaller-sized-graphene-supported electrode exhibited its highest current density with higher mass loading in the thicker films by enabling facile mass transfer through increased diffusion pathways. These findings of the tortuous-path effect on the electrocatalytic electrode supported by varying sized graphene provide new insights and a novel design principle into electrode engineering that will be beneficial for the development of effective electrocatalysts.