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Defective RuO2 possesses excellent initial activity toward oxygen evolution reaction in acidic water electrooxidation due to the involvement of lattice oxygens, which, however, is the very reason for an accelerated dissolution of Ru species. Therefore, it is crucial to steer the electrochemical oxygen evolution to adsorbate evolution mechanism (AEM) for improved durability of RuO2 phase in acidic electrolytes. Herein, we developed a method to mix Pt atoms with RuO2 matrix in a controlled manner by exploiting the oxophilicity of certain first-row transition metals in pulling out the Pt atoms in Pt-based nanorod@Ru under oxidative conditions. The resulting nanorod-shaped PtCo-RuO2/C showed 212.6 ± 5.3 mV overpotential at 10 mA cm-2 in a half-cell test and exhibited mass activity and long-term stability that greatly surpass those of Pt-RuO2/C and commercial Ir/C. Microscopic and spectroscopic analyses and density functional theory calculation of the nanocatalysts before and after OER cycles were conducted to scrutinize the role of Pt dopants for the observed durability and activity, revealing that Pt dopants promote *OOH adsorption and deprotonation, thereby limiting Ru overoxidation during OER cycles. When the PtCo-RuO2/C was applied to a proton-exchange membrane water electrolyzer, it showed a single-cell performance of 3.7 A mgRu+Pt-1 at 2.0 V, which greatly outperforms the commercial IrO2.

As the demand for green hydrogen (H2) rapidly increases, the development of water electrolysis technology has been receiving great attention. Indeed, recent remarkable advances in catalyst materials increased the feasibility of water electrolysis for a future H2 economy and technology. In this review, we summarize representative non-precious group metal-based materials for achieving active and stable water electrolysis performances. Our comprehensive range of the state-of-the-art catalysts includes doped carbon catalysts, metal borides, metal carbides, metal oxides, metal phosphides, metal sulfides, and single-atom catalysts. For each class of materials, we focus on the synthesis and catalytic performances of the state-of-the-art materials toward water electrolysis and present the current challenges and outlooks of such materials, along with prospective insights to develop and realize practical systems.

Deep learning methods have been developed, used in various fields, and they have shown outstanding performances in many cases. Many studies predicted a daily stock return, a classic example of time-series data, using deep learning methods. We also tried to apply deep learning methods to Korea’s stock market data. We used Korea’s stock market index (KOSPI) and several individual stocks to forecast daily returns and directions. We compared several deep learning models with other machine learning methods, including random forest and XGBoost. In regression, long short term memory (LSTM) and gated recurrent unit (GRU) models are better than other prediction models. For the classification applications, there is no clear winner. However, even the best deep learning models cannot predict significantly better than the simple base model. We believe that it is challenging to predict daily stock return data even if we use the latest deep learning methods.

Etching is an effective technique to expose catalytically active sites on the surface of nanocrystals by modifying the surface structure and composition. In this review, various physical and chemical etching methods, specifically developed for nanocrystal systems, as well as their advantages and disadvantages, are introduced. The surface changes in the etched nanocrystals are discussed in view of their impact on catalytic activity and stability to understand the relationship between the nanosurface and catalytic performance. Furthermore, we discuss the standing challenges and provide future research directions in this relevant field, which would lead to fruitful outcomes in developing highly stable and active electrocatalysts for sustainable energy technologies.

The development of electrochemical energy conversion and storage technologies is pivotal to the full-fledged utilization of renewable energy sources. The successful commercial application of water electrolysis to produce hydrogen gas, in particular, requires highly active electrocatalysts that can operate for prolonged periods. However, the high activity and high durability of electrocatalysts are often mutually exclusive. Recent studies have demonstrated that vacancy engineering might effectively modulate the electronic structures of catalysts, which can lead to high catalytic activity. Furthermore, it has been shown that vacancies are closely related to catalyst stability under operational conditions. To understand the benefits of vacancies in the catalyst structures, we discuss the recent advances in the development of vacancy-engineered catalysts for water electrolysis. In addition, we discuss the present limitations in this nascent field and provide directions for valuable future research.

Highly efficient and economically sustainable hydrogen production via electrocatalytic water splitting can be realized by the advent of active and durable electrocatalysts toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Multimetallic nanoframe structures have received great attention as promising electrocatalysts for these reactions, because their inherent high surface area and tunable surface energy states are beneficial to the electrocatalyst performance. We envisaged that the stability and activity of multimetallic nanoframe catalysts could be simultaneously augmented by introducing an additional structural feature of activity-enhancing lattice mismatch via formation of a structure-fortifying core–shell structure. Herein, we successfully demonstrate that hemi-core@frame AuCu@IrNi nanocrystals, possessing structural features of both nanoframe and core–shell, are active and durable bifunctional catalysts toward both the OER and HER under acidic conditions. The hemicore@frame AuCu@IrNi nanocrystals exhibit superior efficient electrocatalytic performance toward the overall water splitting reaction, and show 355 mV overpotential at the current density of 10 mA cm−2 in a 0.5 M H2SO4 electrolyte. The robustness of the catalysts was also verified through the long-term stability test.

Efficient electrocatalysts for energy conversion in general, and fuel cell operation and water electrolysis in particular, are pivotal for carbon-free hydrogen production. While the requirements of successful electrocatalysts include a high number density of catalytically active sites, high surface-to-volume ratio, inherently high catalytic activity, and robustness of the catalyst surface structure under harsh operating conditions, it is extremely difficult to synthesize nanocatalysts that could possess all these structural characteristics. Nanotemplate-mediated synthesis, namely, the coating or filling of a template with a desired material phase followed by the removal of the template, has captured the interest of researchers because of the ease of creating hollow-structured nanocatalysts with a high surface to volume ratio. Recent studies, however, have revealed that nanotemplates could be more than just passive supports because they greatly affect catalytic performance by creating an unusual synergy between the substrate and catalyst and by providing dopants to the actual catalyst phase owing to their reactive nature. In this review, we discuss the most notable recent advances in the nanotemplate-based synthesis of electrocatalysts as well as the unusual effects of nanotemplates on the performance of nanocatalysts. We also provide an outlook for this fledgling field so that future research efforts could be focused on the development of practically useful electrocatalysts that could shape the future of energy technologies.

Electrochemical reduction of carbon dioxide (CO

Electrochemical reduction of carbon dioxide (CO2 RR) product distribution has been identified to be dependent on various surface factors, including the Cu facet, morphology, chemical states, doping, etc., which can alter the binding strength of key intermediates such as *CO and *OCCO during reduction. Therefore, in-depth knowledge of the Cu catalyst surface and identification of the active species under reaction conditions aid in designing efficient Cu-based electrocatalysts. This progress report categorizes various Cu-based electrocatalysts into four main groups, namely metallic Cu, Cu alloys, Cu compounds (Cu + non-metal), and supported Cu-based catalysts (Cu supported by carbon, metal oxides, or polymers). The detailed mechanisms for the selective CO2 RR are presented, followed by recent relevant developments on the synthetic procedures for preparing Cu and Cu-based nanoparticles. Herein, the potential link between the Cu surface and CO2 RR performance is highlighted, especially in terms of the chemical states, but other significant factors such as defective sites and roughened morphology of catalysts are equally considered during the discussion of current studies of CO2 RR with Cu-based electrocatalysts to fully understand the origin of the significant enhancement toward C2 formation. This report concludes by providing suggestions for future designs of highly selective and stable Cu-based electrocatalysts for CO2 RR.