Search

Compared to Ru single atom catalyst, hetero-RuM (M = Fe, Os, and Ir) double atom catalysts showed improved N2RR activity with the help of dxz and dxy bonding orbital, caused by strain, dopant and configurational effects.

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.

Herein, we report the significance of posttreatment in the design of high-performance Fe-N-C-type catalysts for oxygen reduction reaction (ORR). Enhancing the catalytic performance of Fe-N-C requires a postprocess for removing the aggregated iron species formed during high-temperature pyrolysis since they have a negative effect on ORR. We were able to obtain a catalyst precursor for the Fe-N-C reaction via pyrolysis with iron-adsorbed 1,8-diaminonaphthalene (FeDN), which was then treated with a concentrated HCl solution for the removal of the aggregated iron species produced. The HCl-treated FeDN was subsequently annealed at various temperatures to investigate the effect of the annealing process on the physical properties and ORR performance. The annealing temperature was a critical factor affecting the residual contents of impurities, as well as the active component and the electronic state of nitrogen. We also examined the influence of different types of acid (HCl, H2SO4, and HNO3) on the catalytic performance. The type of acid used for removing aggregated iron species had an impact on both the Fe contents and the relative nitrogen species content. Among the catalysts tested, the catalyst prepared by annealing the HCl-treated FeDN at 700°C had the best ORR performance. Although its initial ORR performance in acidic conditions was lower than that of a commercial Pt/C, it was more durable. In alkaline conditions, it delivered a comparable initial ORR performance to Pt/C and also exhibited higher durability.

Electrochemical devices are constructed for continuous syngas (CO + H2) production with controlled selectivity between CO2 and proton reduction reactions. The ratio of CO to H2, or the faradaic efficiency toward CO generation, was mechanically manipulated by adjusting the space volume between the cathode and the polymer gas separator in the device. In particular, the area added between the cathode and the ion-conducting polymer using 0.5 M KHCO3 catholyte regulated the solution acidity and proton reduction kinetics in the flow cell. The faradaic efficiency of CO production was controlled as a function of the distance between the polymer separator and cathode in addition to that manipulated by the electrode potential. Further, the electrochemical CO2 reduction device using Au NPs presented a stable operation for more than 23 h at different H2:CO production levels, demonstrating the functional stability of the flow cell utilizing the mechanical variable as an important operational factor.

Developing a method for fabricating high-efficient and low-cost fuel cells is imperative for commercializing polymer electrolyte membrane (PEM) fuel cells (FCs). This study introduces a mechanical and chemical modification technique using the oxygen plasma irradiation process for hydrocarbon-based (HC) PEM. The oxygen functional groups were introduced on the HC-PEM surface through the plasma process in the controlled area, and microsized structures were formed. The modified membrane was incorporated with plasma-treated electrodes, improving the adhesive force between the HC-PEM and the electrode. The decal transfer was enabled at low temperatures and pressures, and the interfacial resistance in the membrane-electrode assembly (MEA) was reduced. Furthermore, the micropillar structured electrode configuration significantly reduced the oxygen transport resistance in the MEA. Various diagnostic techniques were conducted to find out the effects of the membrane surface modification, interface adhesion, and mass transport, such as physical characterizations, mechanical stress tests, and diverse electrochemical measurements.

A spherical hollow carbon framework decorated with functional heteroatoms is designed and synthesized using ultrasonic spray pyrolysis as a potential anode material for lithium metal batteries (LMBs). The pore structure of the hollow carbon framework can be tailored by melamine, which is a functional additive for integrating abundant nanopores and the uniform decoration of heteroatoms in the structure. The large surface area and pore volume of the hollow carbon framework offer enhanced reversibility and capability for metallic Li storage. In addition, the dendritic growth of Li and volume changes induced by repeated Li plating and stripping can be effectively suppressed during cycling. More importantly, atomic-scale decorations of heteroatoms can effectively lower the overpotential for the nucleation and growth of metallic Li inside the hollow carbon framework. It is mainly responsible for improving the cycle performance and rate capability, even at a high current density. Finally, the hollow carbon framework anode shows stable behavior toward Li plating and stripping without significant capacity fading in the LMBs than conventional Li metal anodes.

The colloidal Langmuir–Blodgett coating process is used to fabricate Au-covered silica sphere monolayer (Au film over silica nanosphere (AuFON)) and study the effects of silica diameter on surface plasmon resonance (SPR) sensing sensitivity. The resulting hexagonal close-packed (HCP) monolayers are prepared with silica sphere diameters of 200, 400, 700, and 1000 nm. In SPR sensing applications, the optical properties of Au-covered silica sphere monolayer are evaluated by measuring normal-incidence reflection spectra and sensing tests. The high sensitivity (nm/RIU) is observed in silica sphere diameter (1000 > 700 > 400 > 200 nm) and plasmon mode (dipole > Fano resonance (FR) > and high order) while the highest sensitivity is 968 nm/RIU (dipole mode, 1000 nm of silica sphere diameter). 3-D Finite Difference Time Domain (FDTD) simulation shows a sensitivity trend similar to the experimental results.

Recent advances in electrochemical desalination techniques have paved way for utilization of saline water. In particular, capacitive deionization (CDI) enables removal of salts with high energy efficiency and economic feasibility, while its applicability has been challenged by degradation of carbon electrodes in long-term operations. Herein, we report a thorough investigation on the surface electrochemistry of carbon electrodes and Faradaic reactions that are responsible for stability issues of CDI systems. By using bare and membrane CDI (MCDI) as model systems, we identified various electrochemical reactions of carbon electrodes with water or oxygen, with thermodynamics and kinetics governed by the electrode potential and pH. As a result, a complete overview of the Faradaic reactions taking place in CDI was constructed by tracing the physicochemical changes occurring in CDI and MCDI systems.

A simple wet-chemical route for the preparation of core-shell-structured catalysts was developed to achieve high oxygen reduction reaction (ORR) activity with a low Pt loading amount. Nickel nitride (Ni3N) nanoparticles were used as earth-abundant metal-based cores to support thin Pt layers. To realize the site-selective formation of Pt layers on the Ni3N core, hydrogen molecules (H2) were used as a mild reducing agent. As H2 oxidation is catalyzed by the surface of Ni3N, the redox reaction between H2 and Pt(IV) in solution was facilitated on the Ni3N surface, which resulted in the selective deposition of Pt on Ni3N. The controlled Pt formation led to a subnanometer (0.5-1 nm)-thick Pt shell on the Ni3N core. By adopting the core-shell structure, higher ORR activity than the commercial Pt/C was achieved. Electrochemical measurements showed that the thin Pt layer on Ni3N nanoparticle exhibits 5 times higher mass activity and specific activity than that of commercial Pt/C. Furthermore, it is expected that the proposed simple wet-chemical method can be utilized to prepare various transition-metal-based core-shell nanocatalysts for a wide range of energy conversion reactions.

The development of oxygen reduction reaction (ORR) catalysts is critical for energy conversion technologies such as fuel cells. This paper proposes an approach to synthesize a hollow-sphere nitrogen-doped carbon shell loaded with cobalt nanoparticles derived from a polystyrene@bimetallic zeolitic imidazolate framework (PS@BMZIF) core@shell, which exhibits high activity as an ORR catalyst. The ORR activity can be enhanced by performing carbonization in the presence of hydrogen, resulting in the growth of additional carbon nanotubes on the hollow-sphere porous carbon shell (h_CoNC/CNT) derived from the PS@BMZIF. The electrocatalyst obtained exhibits excellent ORR activity with a half-wave potential of 0.894 V and long-term stability for 5000 cycles in alkaline media. The h_CoNC/CNT catalyst is applied to the membrane electrode assembly of an anion exchange membrane fuel cell, where it demonstrates a performance of 140 mA/cm2 at 0.6 V and 133 mW/cm2 at the maximum power density and improves mass transfer. The exceptional electrochemical properties of h_CoNC/CNT can be attributed to its desirable hollow-sphere structure with CNTs and the adjustment of efficient active sites of the nitrogen-doped porous material. These findings suggest a potential approach by which to select the structure of the ZIFs and control the pyrolysis condition for ZIF-derived ORR electrocatalysts.

Interface engineering based on the design and fabrication of micro/nanostructures has received much attention as an effective way to improve the performance of polymer electrolyte membrane (PEM) fu...

Currently, efficient hydrogen production via water electrolysis is hindered by the insufficient performance, high cost, and complex fabrication procedure of the hydrogen evolution reaction (HER) electrode. Herein, a facile fabrication method consisting of electrodeposition and a subsequent electrochemical etching process is proposed for high-performance Mo oxide-decorated NiMo (MoO3–MoO2@NiMo) heterostructure catalysts supported by carbon paper. By controlling the conditions used in electrodeposition, the composition and morphology of NiMo deposits could be manipulated. The parameters in the following etching process could be further adjusted to tune the MoO3–MoO2@NiMo heterostructure catalysts, with a significant effect on the intrinsic HER activity. Owing to the synergetic effect of the interface with a roughened morphology, the optimized catalyst exhibited Pt-like activity in the universal pH range. In particular, the HER overpotentials at −10 mA cm−2 are 27.9, 82.6, and 33.4 mV in 0.5 M H2SO4, 1.0 M PBS, and 1.0 M NaOH electrolytes, respectively, which mostly exceed the results for state-of-the-art catalysts. The present strategy for preparing high-performance MoO3–MoO2@NiMo heterostructure electrodes at room temperature and ambient pressure could be expanded to explore elemental synergy in other metal oxide@metal heterostructure electrodes.

The development of non Pt-based catalysts (non-PBCs) that show excellent oxygen reduction reaction (ORR) activity for high-performance Zn–air battery (ZAB) and anion exchange membrane fuel cell (AEMFC) is highly necessitated. Here, the unprecedented single-atom ORR activity of Fe, Si, and N co-doped carbon (FeSiNC) supported on 3D interconnected mesoporous carbons (25 and 50 nm) derived from silica templates is reported. Si moieties connected to a carbon surface were involved in the formation of an atomically distributed FeSixN4−x site through substitution of Si at the N position in the Fe–N4 site, which is the ORR active site of the conventional FeNC. FeSiNC with its larger mesopore (50 nm) exhibits outstanding ORR activity comparable to the most efficient non-Pt-based catalysts and enhanced single-cell performances due to its enhanced mass-transport property. According to theoretical calculations, the ORR activity is originated from not only FeSixN4−x sites located at the basal plane and inter-edge sites, but also C sites adjacent to the Si dopant in both edge and basal regions. Therefore, this study provides a facile strategy toward the rational design of inexpensive and highly active ORR catalysts applicable to single-cell devices.

The development of Pt-based alloy nanoparticles has contributed to improving fuel cell performance. Nevertheless, the commercialization of the catalysts is limited due to structural stability issues. To enhance the durability of Pt-based alloy catalysts, carbon-encapsulated nanoparticles have been widely studied. However, fine-tuning the carbon shell structure at the atomic scale remains a challenge when adopting a typical top-down approach, which involves a high-temperature graphitization process after polymer coating. Here, we propose a bottom-up approach to carbon encapsulation of Pt3Fe1 nanoparticles. Using extremely small amounts of carbon sources produced by the decomposition of organic ligands in metal precursors, carbon-encapsulated Pt3Fe1 nanoparticles with ultrathin carbon shells are fabricated without additional polymer coating process. Furthermore, the pore structure of the carbon shells is rationally modulated at the sub-nm level without changing the particle size via carbon etching using H2 gas. In-depth studies prove that the fine-tuned carbon shell structure has a significant effect on the activity and durability of Pt3Fe1 nanoparticles. Using the testing protocol suggested by the US Department of Energy, a target-customized carbon shell structure has been discovered that satisfies the 2025 targets of “

Hollow Pt-based nanoparticles are known to possess the properties of high electrocatalytic activity and durability. Nonetheless, their practical applications as catalytic materials are limited because of the requirement for exhaustive preparation. In this study, we prepared carbon-supported hollow PtNix (x = the moles of the Ni precursor to the Pt precursor in the catalyst preparation step) catalysts using a one-step preparation method, which substantially reduced the complexity of the conventional method for preparing hollow Pt-based catalysts. In particular, this hollow structure formation mechanism was proposed based on extensive characterizations. The prepared catalysts were examined to determine if they could be used as electrocatalysts for the oxygen reduction reaction (ORR). Among the investigated catalysts, the acid-treated hollow PtNi3/C catalyst demonstrated the best ORR activity, which was 3 times higher and 2.3 times higher than those of the commercial Pt/C and acid-treated particulate PtNi3/C catalysts, respectively.

Electrochemical nitrogen reduction reaction (NRR) is a promising method for energy-efficient and low-emission NH3 production. Herein, we report electrochemical NH3 production using a copper sulfide...

The electrode ionomer is a key factor that significantly affects the catalyst layer morphology and fuel cell performance. Herein, sulfonated poly(arylene ether sulfone)-based electrode ionomers with polymers of various molecular weights and alcohol/water mixtures were prepared, and those comprising the alcohol/water mixture showed a higher performance than the ones prepared using higher boiling solvents, such as dimethylacetamide; this is owing to the formation of the uniformly dispersed ionomer catalyst layer. The relation between ionomer molecular weight for the same polymer structure and the sulfonation degree was investigated. Because the chain length of polymer varies with molecular weight and chain entanglement degree, its molecular weight affects the electrode morphology. As the ionomer covered the catalyst, the agglomerates formed were of different morphologies according to their molecular weight, which could be deduced indirectly through dynamic light scattering and scanning electron microscopy. Additionally, the fuel cell performance was confirmed in the current-voltage curve.

Electrode structure improvement is one of the most promising paths for improving the durability of polymer electrolyte membrane fuel cells (PEMFCs). As strategies to prevent structural deformation and enhance the durability of membrane electrode assemblies (MEAs) with structurally ordered PtCo/C-based cathodes, we evaluated the effect of hot pressing and reinforcing the electrode's structure by increasing the ionomer content. Even though the initial performances of the hot-pressed MEA (HP) and the MEA with extra cathode ionomer (EI) were lower than that of the conventional MEA (CE) by 13.6% and 19.1%, respectively, CE degraded much more significantly than HP and EI after an accelerated degradation test. Therefore, HP and EI could deliver significantly higher single cell performances than CE (22.7% and 43.7%, respectively). The improvements in the durability of HP and EI could be correlated with the structural stability which could be evaluated by structure and electrochemical analysis including electrochemical impedance spectroscopy.

A simple and facile way of modifying commercial membranes for effective fuel cell operation under elevated temperature/low relative humidity conditions has been developed. Instead of using the conventional casting and evaporation method involving the mixed Nafion® ionomer and inorganic fillers, a TiO2/Nafion® composite membrane was fabricated by transferring uniformly constructed porous TiO2 layers from a Si wafer to the Nafion® membrane via spin-coating, followed by a thermal imprinting process. From the process, filler agglomeration was prevented during the solvent evaporation, which secured water retention effect of the hygroscopic TiO2 layers. Furthermore, the prepared TiO2/Nafion® composite membrane was subjected to an additional prism patterning process to provide more proton pathways by enlarging the interfacial surface area between the composite membrane and the catalyst layer, and offset the reduced proton conductivity due to insertion of the inorganic fillers. The modified membrane exhibited highly improved performance compared to the pristine Nafion® 211 membrane under elevated temperature/low humidity conditions.

The hydrogen economy expansion triggered studies on the durability of hydrogen-powered proton-exchange membrane fuel cells (PEMFCs), which revealed that their performance is largely hindered by the...

Despite breakthroughs in the activity of electrocatalysts for the oxygen reduction reaction (ORR), the development of nanoscale ORR electrocatalysts is still hindered by their instability. Here, to...

In many catalyst systems, including fuel cell applications, control of the catalyst surface composition is important for improving activity since catalytic reactions occur only at the surface. However, it is very difficult to modify the surface composition without changing the morphology of metal nanoparticles. Herein, carbon-supported Pd3Au1 nanoparticles with uniform size and distribution are fabricated by tert-butylamine reduction method. Pd or Au surface segregation is induced by simply heating as-prepared Pd3Au1 nanoparticles under CO or Ar atmosphere, respectively. Especially, CO-induced Pd surface segregation allows the alloy nanoparticles to have a Pd-rich surface, which is attributed to the strong CO binding energy of Pd. To demonstrate the change in surface composition of Pd3Au1 alloy catalyst with the annealing gas species, the oxygen reduction reaction performance is investigated and consequently, Pd3Au1 catalyst with the highest number of surface Pd atoms indicates excellent catalytic activity. Therefore, the present work provides insights into the development of metal-based alloys with optimum structures and surface compositions for various catalytic systems.

We demonstrate that control of the defect level on carbon materials is effective for enhancing the oxygen reduction reaction (ORR) performance of nonprecious-metal catalysts. Vapor-grown carbon nanofiber (VGCNF) with high crystallinity and high electronic conductivity was chosen as the substrate of our ORR catalysts. To induce defects on the VGCNF, it was subjected to ball-milling for various controlled times, yielding BMx-VGCNF (x represents the ball-milling time, 0-6 h). The defect level introduced on the VGCNF was effectively regulated by controlling the ball-milling time. Although the density of defect sites increased with increasing ball-milling time, the surface area was high-est in BM2-VGCNF. Nonprecious-metal ORR catalysts (BMx-Fe-VGCNF) were prepared by NH3 pyrolysis of Fe-ion-adsorbed BMx-VGCNF. The ball-milling of VGCNF was effective to introduce nitrogen onto the catalyst. In particular, the controlled ball-milling was important to generate highly active sites on the catalyst surface. Among the catalysts studied, BM2-Fe-VGCNF exhibited the best ORR performance, which was 2.5-times greater than that of BMx-Fe-VGCNF (x=4, 6).