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To overcome inherent limitations of molybdenum carbide (MoxC) for hydrogen evolution reaction (HER), i.e., low density of active site and nonideal hydrogen binding strength, we report the synthesis of valence-controlled mesoporous MoxC as a highly efficient HER electrocatalyst. The synthesis procedure uses an interaction mediator (IM), which significantly increases the density of active site by mediating interaction between PEO-b-PS template and Mo source. The valence state of Mo is tuned by systematic control of the environment around Mo by controlled heat treatment under air before thermal treatment at 1100 °C. Theoretical calculations reveal that the hydrogen binding is strongly influenced by Mo valence. Consequently, MoxC achieves a significant increase in HER activity (exceeding that of Pt/C at high current density ∼35 mA/cm2in alkaline solution). In addition, a volcano-type correlation between HER activity and Mo valence is identified with various experimental indicators. The present strategies can be applied to various carbide and Mo-based catalysts, and the established Mo valence and HER relations can guide development of highly active HER electrocatalysts.

Partially hydrous RuO2nanocluster embedded in a carbon matrix (x-RuO2@C with x = hydration degree = 0.27or 0.27@C) is presented as a bifunctional catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for water splitting. Symmetric water electrolyzers based on 0.27-RuO2@C for both electrodes showed smaller potential gaps between HER and OER at pH 0, pH 14 and even pH 7 than conventional asymmetric electrolyzers based on two different catalysts (Pt/C || Ir/C) that have been known as the best catalysts for HER and OER respectively. Moreover, 0.27-RuO2@C showed another bifunctional electroactivity for fuel cell electrochemistry involving hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) that are the backward reactions of HER and OER respectively. Pt-level HOR electroactivity was obtained from 0.27-RuO2@C, while its ORR activity was inferior to that of Pt with 200 mV higher overpotential required. The tetra-functionality of 0.27-RuO2@C showed the possibility of realizing single-catalyst regenerative fuel cells.

Ionic polymer–metal composites (IPMCs) have been proposed as biomimetic actuators that are operable at low applied voltages. However, the bending strain and generating force of the IPMC actuators have generally exhibited a trade-off relationship, whereas simultaneous enhancement of both the qualities is required for their practical applications. Herein, a significant improvement in both the strain and force of the IPMC actuators is achieved by a facile approach, exploiting thickness-controlled ion-exchange membranes and nanodispersed metal electrodes. To guarantee a large generating force of the IPMC actuators, ultrathick ion-exchange membranes are prepared by stacking pre-extruded Nafion films. Metal electrodes with a nanodispersed structure are formed on the membranes via alcohol-assisted electroless plating, which allows increased capacitance and facilitated ion transport. The resulting actuators exhibit greatly enhanced electromechanical properties, including an approximately four times larger strain and two times larger force compared to those of actuators having the conventional structure. Moreover, the ability to lift 16 coins (a weight of 124 g) has been successfully demonstrated using ultrathick IPMC actuators, which shows great promise in realizing artificial muscles.

Electrochemical energy storage devices based on electric double layer capacitors (EDLCs) have received considerable attention due to their high power density and potential for obtaining improved energy density in comparison to the lithium ion battery. Ordered mesoporous carbon (OMC) is a promising candidate for use as an EDLC electrode because it has a high specific surface area (SSA), providing a wider charge storage space and size-controllable mesopore structure with a long-range order, suppling high accessibility to the electrolyte ions. However, OMCs fabricated using conventional methods have several drawbacks including low electronic conductivity and long ionic diffusion paths in mesopores. We used nickel nanofoam, which has a relatively small pore (sub-100 nm to subμm) network structure, as a current collector. This provides a significantly shortened electronic/ionic current paths and plentiful surface area, enabling stable and close attachment of OMCs without the use of binders. Thus, we present hierarchical binder-free electrode structures based on OMC/Ni nanofoams. These structures give rise to enhanced specific capacitance and a superior rate capability. We also investigated the mesopore structural effect of OMCs on electrolyte transport by comparing the capacitive performances of collapsed lamellar, cylindrical, and spherical mesopore electrodes. The highly ordered and straightly aligned cylindrical OMCs exhibited the highest specific capacitance and the best rate capability.

Although the electrochemical hydrogen evolution reaction (HER) has been intensively investigated for decades as a promising hydrogen production source, its economic feasibility is still questionable because of the high cost of Pt-based electrocatalysts. Transition metal phosphides are potential replacements for Pt; however, a fundamental understanding of the active catalyst site chemistry is still lacking. Such an understanding is crucial to design robust catalytic materials. The aim of this study is to rationalize the HER on the active sites of nickel phosphide (Ni2P) nanowires. Using experimental and theoretical analyses, it can be concluded that the active site of Ni2P nanowires is an exposed Ni3P2surface generated by the oxygenated Ni3P_P surface created during the HER. This work is a breakthrough in the efficient design of phosphide-based non-Pt catalysts for electrochemical hydrogen production.

The membrane electrolyte assembly (MEA) designed in this study utilizes a double-layered cathode: an inner catalyst layer prepared by a conventional decal transfer method and an outer catalyst layer directly coated on a gas diffusion layer. The double-layered structure was used to improve the interfacial contact between the catalyst layer and membrane, to increase catalyst utilization and to modify the removal of product water from the cathode. Based on a series of MEAs with double-layered cathodes with an overall Pt loading fixed at 0.4 mg cm–2and different ratios of inner-to-outer Pt loading, the MEA with an inner layer of 0.3 mg Pt cm–2and an outer layer of 0.1 mg Pt cm–2exhibited the best performance. This performance was better than that of the conventional single-layered electrode by 13.5% at a current density of 1.4 A cm–2.

Direct electrostatic interactions between a charged Pt surface and oppositely charged spectator ions are utilized for the enhancement of oxygen reduction reaction (ORR) activity in both KOH and H3PO4solutions. Zwitterionic L-cysteine molecules functionalized on a Pt surface are turned outwards to afford differing surface charges in either alkaline (−) or acid solutions (+). In KOH solution, this leads to the selective impediment of interactions between OH−and K+with the Pt surface through repulsive and attractive interactions of the negatively charged –COO−group of L-cysteine, respectively. In H3PO4solution, the phosphoric acid molecule and its anion are effectively captured by the positively charged –NH3+moieties of L-cysteine. Behaviors of the spectator species hindering the ORR are systematically controlled through direct electrostatic interactions with the functional groups of L-cysteine in each electrolyte, resulting in a Janus Pt catalyst for superior ORR in both alkaline and acid electrolytes.

The thermal annealing process is a common treatment used after the preparation step to enhance the electrocatalytic properties of the oxygen reduction reaction (ORR). The structure of a Pt-based bimetallic nanoparticle, which is significantly affected by the catalytic properties, is reconstructed by thermal energy. We investigated the effect of structural reconstruction induced by thermal annealing on the improvement of the ORR using various physical and electrochemical methods. We found that the structural evolution of PtNi nanoparticles, i.e., the Pt–Ni ordering with the Pt shell and the surface reorientation into the (111) facet, is the source of the enhanced ORR activity as well as electrochemical stability through the thermal annealing. This result confirms the crucial factors for the ORR properties by the thermal annealing process and proposes a way to design advanced electrocatalysts.

Reversible surface segregation of Pt in Pt3Au/C catalysts was accomplished through a heat treatment under a CO or Ar atmosphere, which resulted in surface Pt segregation and reversed segregation, respectively. The Pt-segregated Pt3Au/C exhibited a significantly improved oxygen reduction reaction (ORR) activity (227 mA/mgmetal) compared to that of commercial Pt/C (59 mA/mgmetal). For the Pt-segregated Pt3Au/C, the increased OH-repulsive properties were validated by a CO bulk oxidation analysis and also by density functional theory (DFT) calculations. Interestingly, the DFT calculations revealed that the binding energy for Pt-segregated Pt3Au (111) surfaces was 0.1 eV lower than that for Pt (111) surfaces, which has been previously reported to exhibit the optimum OH binding energy for the ORR. Therefore, the reversible surface segregation is expected to provide a practical way to control the surface states of Pt–Au bimetallic catalysts to enhance ORR activity. In addition, the Pt-segregated Pt3Au/C showed excellent electrochemical stability, as evidenced by its high-performance retention (96.4%) after 10 000 potential cycles, in comparison to that of Pt/C (55.3%).

It is demonstrated that the electroactivity of the oxygen reduction reaction (ORR) of Pt depends on the structure of a support. Highly conductive two-dimensional titanium carbide (Ti3C2) was selected as the support for Pt because of the expected strong metal-support interaction (SMSI) between Pt and Ti. To control the edge-to-basal ratio, the number of Ti3C2layers was modulated by exfoliation. Pt nanoparticles (4 nm) were loaded on three different Ti3C2supports including multi-, few-, and mono-layered Ti3C2(22L-, 4L-, and 1L-Ti3C2, respectively). The edge-to-basal ratio of layered Ti3C2increased as the number of layers increased. The edge-dominant support (22L-Ti3C2) donated more electrons to Pt than the basal-dominant supports (4L-Ti3C2and 1L-Ti3C2). As a result, electron-rich Pt with less d-band vacancies (e.g., Pt/22L-Ti3C2) showed higher ORR activity. In addition, the electron transfer from the support to Pt inducing the strong interaction between Pt and Ti improved the durability of the ORR electroactivity of Pt.

We studied the electrochemical synthesis of NH3on Fe–CuS/C catalysts in an alkaline aqueous solution under ambient conditions. The metal chalcogenide catalyst is active in the nitrogen reduction reaction (NRR) for approximately 45 min with an NH3production yield of 16 μg h–1cm–2at −0.4 VRHE, while it decomposes to CuO. The rapid degradation of the catalyst hinders the precise investigation of the NH3production activity in longer time measurements. Herein, the electrochemical NH3production rate is enhanced with increased overpotentials when the degradation effect is mitigated in the measurement, which was difficult to observe in the NRR reports. In the Tafel analysis, the exchange current density, heterogeneous rate constant, and transfer coefficient of the Fe–CuS/C catalyst on the NRR were estimated. When the electrode degradation is mitigated, one of the best NH3production activities among the reported metal sulfide electrochemical NRR catalysts is obtained, which is 42 μg h–1cm–2at −0.6 VRHE.

Oxygen reduction reaction (ORR) kinetics are enhanced in alkaline media. Hence, alternative non-platinum (Pt)-group metal electrocatalysts have been investigated extensively in this medium to compete with Pt in terms of performance and durability. Among various non-Pt catalysts, one of the most popular class of electrocatalysts is iron- and nitrogen-doped carbon-based (Fe–N–C) by the high electrocatalytic activity and selectivity in ORR. However, the inherent catalytic reactivity of such non-Pt electrocatalysts remains inferior to that of state-of-the-art Pt electrocatalysts. Here, we explore the ORR of hollow and urchin-like, three-dimensional (3D) nanostructured Fe–N–Cs prepared via polymerization-induced self-assembly of aniline followed by carbonization. The resulting Fe–N–Cs consist of a hollow microsphere framework coupled with nanorod bundles, and exhibit large surface areas (874 m2g−1), hierarchical cavities, and excellent electrical conductivities (0.63 Scm−1) as electrodes. They are of particular interest as oxygen reduction electrocatalyst for proton exchange membrane fuel cells (PEMFCs). These unique features, which enhance electrocatalytic efficiency, are attributed to efficient mass- and electro-transport ORR kinetics. Electrochemical experiments reveal improved onset (ca. 1.04 V) and half-wave potentials (ca. 0.9 V), which is comparable to those of commercial Pt electrocatalysts. The 3D hierarchical porous network with high interdigitation of well-dispersed nanorod building blocks is thought to be key to facilitating the ORR reaction.

Using extended X-ray absorption fine structure (EXAFS) spectroscopy and cyclic voltammetry (CV) in combination, the fraction of surface Pt atoms poisoned by the phosphoric acid adsorbed (θPA) on Pt/C was analyzed for various electrode potentials (0.35, 0.60, and 0.8 V). The θPAvalues at 0.35 V, 0.6 V, and 0.8 V were determined to be 0.32, 0.45, and 0.38, respectively. The differences in the θPAvalues determined using EXAFS spectroscopy in this study and those estimated from the relative number of phosphoric acid molecules adsorbed are probably attributable to an increase in the number of Pt-O bonds per adsorbed phosphoric acid molecule. This, in turn, is owing to an increase in the degree of electrochemical adsorption with an increase in the potential. That the θPAvalue for the Pt(111) surface at 0.35 V as determined using EXAFS spectroscopy was higher than that estimated through the CV analysis was because of the chemical adsorption and/or electrochemical adsorption of phosphoric acid on the (100) facets and edge sites of the Pt/C surfaces.

The article discusses the issue of liberalization of the capital market in South Korea and the ways in which it can enjoy the benefits of incoming foreign capital without being curbed by it. Financiers are getting eager to invest in Korea's liberalized capital market. As a result, corporate strategies are being formulated with the view of improving management skills. The article refers to the case of KT&G Corp. to illustrate this point.

The hydrogen oxidation reaction activity of sub-monolayer Pt-shell/Pd-core nanoparticles was investigated at a Pt surface concentration of 0 ∼ 5.7%. The nanoparticles were prepared using a colloidal approach. The combination of electrochemical measurements and high resolution-X-ray photoelectron spectroscopy revealed a significant decrease in oxidized Pd atoms (23.4%) with a Pt surface concentration of 1.7% compared with that of Pd/C. X-ray absorption spectroscopy of the Pt LIII edge suggested preferred Pt deposition, which led to more oxidized Pt atoms during Pt shell growth. The exchange current density of the hydrogen oxidation reaction on the electrocatalyst with a Pt surface concentration of 4.9% was 3.5 times higher than that on Pd/C and was comparable with that on Pt surfaces. The changes in hydrogen oxidation reaction apparent enthalpy due to Pt shell growth suggested a rate determining step (RDS) change (Volmer reaction → Tafel reaction) at a Pt surface concentration of 1.7%.

The oxygen reduction activities of platinum and platinum alloy catalysts were evaluated at temperatures up to 150 ?°C in phosphoric acid solution. The oxygen reduction currents and open circuit potentials were measured using chronoamperometry with double potential steps to eliminate the effects of double layer charging currents and metal deactivationcould be eliminated effectively. Based on the mass activity at 0.7 V versus Ag/AgCl, the commercial PtNi catalyst showed higher performances than commercial Pt catalyst at 150?°C. The commercial PtCo catalyst showed high activities at 90?°C and 120?°C. Intermediate temperature fuel cells based on phosphoric acid doped polybenzimidazole membranes were tested with the alloy cathode catalysts. In the case of Pt–Fe alloy an enhanced performance was achieved in comparison to that with Pt carbon catalysts.

Due to the advantage of fuel cells over secondary batteries such as long operation time, many efforts were executed in order to use fuel cells as main power sources of small electronic devices such as laptop computers and mobile phones. For the same reason, fuel cells are promising power sources for the hazardous mission robots. Fuel cells are able to increase their radius action through extension of operation time. Despite this advantage, there still exist technical barriers such as increasing power density, efficient hydrogen storage, and fast startup of the power system. First, in order to increase power density, the united stack including proton exchange membrane fuel cells (PEMFC) and membrane humidifying cells were developed. Also, the hydrogen generating system using NaBH4 solution was employed to store hydrogen effectively. In addition, to shorten start-up time, hybrid control of PEMFC and Li-ion battery was adopted. The approaches mentioned above were evaluated. The developed PEMFC/humidifier stack showed high performance. As compared with full humidification condition by external humidifiers, the performance decrease was only 1% even though hydrogen was not humidified and air was partially humidified. Besides, by integrating the PEMFC and the humidifier into a single stack, considerable space for tubing between them was saved. Also, the hydrogen generator operated well with the PEMFC system and allowed for effective fuel storing and refueling. In addition, due to the efficient hybrid control of PEMFC and battery, start-up time was significantly shortened and capacity of PEMFC was reduced, resulting in compactness of the power system. In conclusion, a 600 W PEMFC power system was developed and successfully operated with the robot. Through development and evaluation of the PEMFC power system, the possibility of PEMFC as a novel power source for the hazardous mission robot was verified.

This paper uses a variety of physicochemical methods to elucidate the mechanism by which cathode inlet relative humidity (RH) degrades a proton exchange membrane fuel cell (PEMFC) during startup–shutdown cycling. The results revealed that the pronounced Pt coarsening (agglomeration)/oxidation/dissolution (detachment) and migration were observed along with corrosion of the carbon support at the majority of cathode catalyst layers when PEMFCs were exposed to a higher cathode inlet RH during 1500 startup–shutdown cycles. These changes contributed to the significant loss of Pt mass available for electrochemical reactions and an active Pt surface area at the cathode, thus decaying the performance of the fuel cell. In addition, the rate of these multiple processes was RH-dependent. However, the degradation at the anode and membrane was not as severe as those observed at the cathode and did not show any dependence on the cathode inlet RH. Based on these results, a modified mechanism for the degradation of the cathode catalyst layer during startup–shutdown cycling of PEMFCs is proposed to explain the effects of RH on fuel cell performance and durability.

This work investigated the effect of cathode inlet relative humidity (RH) on the durability of proton exchange membrane fuel cells (PEMFCs) during startup–shutdown cycling via single-cell experiments. Electrochemical techniques, including measurements of polarization curves, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear sweep voltammetry, were performed to examine the effect of cathode inlet RH on the degradation of PEMFCs. The performance was better for PEMFCs cycled at a lower cathode inlet RH than for those cycled at a higher cathode inlet RH on the order of 050100%. The CV and EIS results showed that as the cathode inlet RH increased, the loss of electrochemically active surface area and the increase in the charge-transfer resistance (Rct)were faster during the startup–shutdown cycling. However, changes in ohmic resistance (Rohm)and hydrogen crossover current density were not detectable, revealing that severe membrane degradation did not occur regardless of the cathode inlet RH during startup–shutdown cycles.

To investigate the effect of an application of a dummy load during the start-up procedure on the degradations of a membrane electrode assembly (MEA) exposed to the 1200 repetitive start-up–shutdown cycling, this paper uses a variety of physicochemical methods such as online CO2analysis, field-emission-scanning electron microscopy, energy dispersive X-ray, electron probe microanalysis, X-ray diffraction, field-emission transmission electron microscopy, selected-area electron diffraction, X-ray photoelectron spectroscopy, Fourier transformation infrared, and inductively coupled plasma. After the 1200 start-up–shutdown cycles, a pronounced particle size growth/agglomeration/oxidation/dissolution of the Pt catalysts and corrosion of the carbon support were observed at the cathode catalyst layer when starting up a proton exchange membrane fuel cell (PEMFC) without a dummy load, which significantly contributed to the losses of active Pt surface area and Pt mass for electrochemical reactions, and thus the degradation of cell performance. However, applying a dummy load during the start-up procedure remarkably mitigated such severe degradations and should be used to improve the durability of MEAs during start-up–shutdown cycling of PEMFCs. Degradations at the anode and membrane were not as severe as those observed at the cathode.

For polymer electrolyte membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) catalyst layers (CLs), a complex capacitance analysis of impedance data was developed to evaluate the catalyst/ionomer interfacial capacitance and ionic resistance of ionomer networks without nonlinear data fitting. First, assuming no faradaic reactions, equivalent circuits for the CLs were suggested, which are similar to electric double-layer capacitor systems with porous carbon electrodes. Then, with the simulated complex capacitances, it was confirmed that the plots of the real and imaginary parts as a function of ac frequency are determined by the catalyst/ionomer interfacial capacitances and the ionic resistances time constants, which are important characteristics for high fuel cell performances. Experimentally, the condition of no faradaic reactions was realized by supplying nitrogen or water to the cathodes instead of air and by fixing the dc potential at 0.4 V during the impedance measurements. By performing a complex capacitance analysis, the interfacial capacitances and ionic resistances of PEMFC membrane electrode assemblies (MEAs) can be obtained at various relative humidities, proving that the catalytic activity in fuel cell operation depends on ionic resistances as well as on the catalyst/ionomer interfacial area. The effects of various MEA preparation methods on the ionomer distributions and DMFC performances were analyzed by a complex capacitance analysis.

For PEMFC and DMFC catalyst layers, a complex capacitance analysis of impedance data was developed to evaluate the catalyst/ionomer interfacial capacitance and ionic resistance of ionomer networks, without non-linear data fitting. Assuming no Faradaic reactions, equivalent circuits for the catalyst layers were suggested, and it was confirmed that the plots of the real and imaginary parts as a function of ac frequency are determined by the catalyst/ionomer interfacial capacitances and RC time constants, which are important characteristics for high fuel cell performances. By performing a complex capacitance analysis, the interfacial capacitances and ionic resistances of PEMFC MEAs can be experimentally obtained at various relative humidities, proving that the catalytic activity in fuel cell operation depends on ionic resistances as well as on the catalyst/ionomer interfacial area. In addition, the effects of various MEA preparation methods on the ionomer distributions and DMFC performances were analyzed by a complex capacitance analysis.

Various polymer electrolyte membrane fuel cell (PEMFC) startup procedures were tested to explore possible techniques for reducing performance decay and improving durability during repeated startup–shutdown cycles. The effects of applying a dummy load, which prevents cell reversal by consuming the air at the cathode, on the degradation of a membrane electrode assembly were investigated via single-cell experiments. Electrochemical techniques, including measurement of polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry, and linear sweep voltammetry, were employed to investigate the degradation of the PEMFCs. The results showed that application of a dummy load during the startup procedure significantly reduced the performance decay, the decrease in the electrochemically active surface area, and the increase in charge-transfer resistance (Rct), which resulted in a dramatic improvement in durability. Our results suggest that starting up PEMFCs while applying a dummy load is an effective method for mitigating performance degradation caused by cell reversal under a repetition of unprotected startup cycles.