Jun Kim

Bio: Jun Kim is an academic researcher from Korea Institute of Science and Technology. The author has contributed to research in topics: Nanocages & Overpotential. The author has an hindex of 8, co-authored 20 publications receiving 357 citations. Previous affiliations of Jun Kim include Korea University.

Hollow nanoparticles as emerging electrocatalysts for renewable energy conversion reactions

Abstract: While the realization of clean and sustainable energy conversion systems primarily requires the development of highly efficient catalysts, one of the main issues had been designing the structure of the catalysts to fulfill minimum cost as well as maximum performance. Until now, noble metal-based nanocatalysts had shown outstanding performances toward the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). However, the scarcity and high cost of them impeded their practical use. Recently, hollow nanostructures including nanocages and nanoframes had emerged as a burgeoning class of promising electrocatalysts. The hollow nanostructures could expose a high proportion of active surfaces while saving the amounts of expensive noble metals. In this review, we introduced recent advances in the synthetic methodologies for generating noble metal-based hollow nanostructures based on thermodynamic and kinetic approaches. We summarized electrocatalytic applications of hollow nanostructures toward the ORR, OER, and HER. We next provided strategies that could endow structural robustness to the flimsy structural nature of hollow structures. Finally, we concluded this review with perspectives to facilitate the development of hollow nanostructure-based catalysts for energy applications.

Rational design of Pt-Ni-Co ternary alloy nanoframe crystals as highly efficient catalysts toward the alkaline hydrogen evolution reaction

Abstract: The rational design of highly efficient electrocatalysts for the hydrogen evolution reaction (HER) is of prime importance for establishing renewable and sustainable energy systems. The alkaline HER is particularly challenging as it involves a two-step reaction of water dissociation and hydrogen recombination, for which platinum-based binary catalysts have shown promising activity. In this work, we synthesized high performance platinum–nickel–cobalt alloy nanocatalysts for the alkaline HER through a simple synthetic route. This ternary nanostructure with a Cartesian-coordinate-like hexapod shape could be prepared by a one-step formation of core–dual shell Pt@Ni@Co nanostructures followed by a selective removal of the Ni@Co shell. The cobalt precursor brings about a significant impact on the control of size and shape of the nanostructure. The PtNiCo nanohexapods showed a superior alkaline HER activity to Pt/C and binary PtNi hexapods, with 10 times greater specific activity than Pt/C. In addition, the PtNiCo nanohexapods demonstrated excellent activity and durability for the oxygen reduction reaction in acidic media.

Hybrid layered double hydroxides as multifunctional nanomaterials for overall water splitting and supercapacitor applications

Abstract: Global demand for energy conversion and storage technologies such as fuel cells, water electrolyzers, batteries, and supercapacitors is increasing, yet their commercial and environmental viability are critically dependent on the performance of their electrode materials and catalysts, which are the indispensable components that drive these systems. Among various materials, layered double hydroxides (LDHs) are considered promising candidates for catalysts and electrodes for electrochemical energy conversion and storage systems. Their diverse range of chemical properties make them highly versatile platforms for developing hybrid nanostructures, including flexible two-dimensional LDH nanostructures with various di-/tri-valent metals. Hybrid LDHs also exhibit unique structural attributes, including 3D hierarchical porous features and heterointerfaces, as well as optimized electrical conductivity and stability, which are crucial to achieving highly efficient multifunctional nanomaterials for electrochemical energy device applications. This review presents recent developments in the design, synthetic routes, structural/chemical modification strategies, and applications of hybrid LDHs as multifunctional nanomaterials for overall water splitting and electrochemical supercapacitors. Recent advances in modification strategies are critically assessed to determine their effect on the physicochemical properties of hybrid LDHs. The hybrid nanostructures' alteration of energy barriers in the electrocatalytic reactions is also discussed. Finally, this review concludes with future outlooks for hybrid LDH nanostructures.

Synthesis of compositionally tunable, hollow mixed metal sulphide CoxNiySz octahedral nanocages and their composition-dependent electrocatalytic activities for oxygen evolution reaction

Abstract: Hollow nanostructures such as nanocages and nanoframes can serve as advanced catalysts with their enlarged active surface areas, and hence they have been of widespread interest. Despite the recent progress in the synthesis of this class of nanomaterials, hollow nanostructures with tunable compositions and controlled morphologies have rarely been reported. Here, we report a facile synthetic route to a series of compositionally tunable, hollow mixed metal sulphide (CoxNiySz) octahedral nanocages. The sulfidation of CoO octahedral nanoparticles generates CoO@CoxSy core-shell octahedra, and the in situ etching of the CoO core and annealing yield Co9S8 (pentlandite) octahedral nanocages (ONC). The addition of a Ni precursor during the etching/annealing process of CoO@CoxSy core-shell octahedra progressively yields hollow ONC structures of Co9-xNixS8, Ni9S8, Ni9S8/β-NiS, and Ni3S2/β-NiS via cation exchange reactions. Mixed cobalt/nickel sulphide, Co9-xNixS8 ONC, shows superior oxygen evolution reaction activity to monometallic sulphide ONC structures, demonstrating the synergy between different metal species.

Recent Advances in Electrocatalytic Hydrogen Evolution Using Nanoparticles.

Abstract: Hydrogen fuel is considered as the cleanest renewable resource and the primary alternative to fossil fuels for future energy supply. Sustainable hydrogen generation is the major prerequisite to realize future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the vital step of water electrolysis to H2 production, has been the subject of extensive study over the past decades. In this comprehensive review, we first summarize the fundamentals of HER and review the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts. We systemically discuss the insights into the relationship among the catalytic activity, morphology, structure, composition, and synthetic method. Strategies for developing an effective catalyst, including increasing the intrinsic activity of active sites and/or increasing the number of active sites, are summarized and highlighted. Finally, the challenges, perspectives, and research directions of HER electrocatalysis are featured.

Electrocatalysts for Hydrogen Evolution in Alkaline Electrolytes: Mechanisms, Challenges, and Prospective Solutions

Abstract: Hydrogen evolution reaction (HER) in alkaline medium is currently a point of focus for sustainable development of hydrogen as an alternative clean fuel for various energy systems, but suffers from sluggish reaction kinetics due to additional water dissociation step. So, the state-of-the-art catalysts performing well in acidic media lose considerable catalytic performance in alkaline media. This review summarizes the recent developments to overcome the kinetics issues of alkaline HER, synthesis of materials with modified morphologies, and electronic structures to tune the active sites and their applications as efficient catalysts for HER. It first explains the fundamentals and electrochemistry of HER and then outlines the requirements for an efficient and stable catalyst in alkaline medium. The challenges with alkaline HER and limitation with the electrocatalysts along with prospective solutions are then highlighted. It further describes the synthesis methods of advanced nanostructures based on carbon, noble, and inexpensive metals and their heterogeneous structures. These heterogeneous structures provide some ideal systems for analyzing the role of structure and synergy on alkaline HER catalysis. At the end, it provides the concluding remarks and future perspectives that can be helpful for tuning the catalysts active-sites with improved electrochemical efficiencies in future.

Recent progress made in the mechanism comprehension and design of electrocatalysts for alkaline water splitting

Abstract: Alkaline water splitting is an attractive method for sustainable hydrogen production. Owing to the sluggish kinetics of alkaline water reduction and oxidation, it is crucial to understand the mechanism of the hydrogen evolution reaction/oxygen evolution reaction (HER/OER) and construct efficient electrocatalysts based on the structure–activity relationship. This review describes the fundamentals of the alkaline HER and OER, the design of noble and nonnoble HER electrocatalysts with low energy barriers, OER electrocatalysts based on binding energy, electronic structure, lattice oxygen, and surface reconstruction as well as the recent developments of bifunctional HER/OER electrocatalysts. Future perspectives towards alkaline water splitting electrocatalysts are also proposed.

Nickel-Based Electrocatalysts for Energy-Related Applications: Oxygen Reduction, Oxygen Evolution, and Hydrogen Evolution Reactions

Abstract: The persistently increasing energy consumption and the low abundance of conventional fuels have raised serious concerns all over the world. Thus, the development of technology for clean-energy production has become the major research priority worldwide. The globalization of advanced energy conversion technologies like rechargeable metal–air batteries, regenerated fuel cells, and water-splitting devices has been majorly benefitted by the development of apposite catalytic materials that can proficiently carry out the pertinent electrochemical processes like oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and water hydrolysis. Despite a handful of superbly performing commercial catalysts, the high cost and low electrochemical stability of precursors have consistently discouraged their long-term viability. As a promising substitute of conventional platinum-, palladium-, iridium-, gold-, silver-, and ruthenium-based catalysts, various transition-metal (TM) i...

Electrocatalysis on Platinum Nanoparticles: Particle Size Effect on Oxygen Reduction Reaction Activity

Abstract: We determined the size-dependent specific and mass activities of the oxygen reduction in HClO(4) solutions on the Pt particles in the range of 1-5 nm. The maximal mass activity at 2.2 nm is well explained based on density functional theory calculations performed on fully relaxed nanoparticles. The presence of the edge sites is the main reason for the low specific activity in nanoparticles due to very strong oxygen binding energies at these sites. Our results clearly demonstrate that the catalytic activity highly depends on the shape and size of the nanoparticles.