Tailoring the Electronic Structure of Nanoelectrocatalysts Induced by a Surface-Capping Organic Molecule for the Oxygen Reduction Reaction

Capping organic molecules, including oleylamine, strongly adsorbed onto Pt nanoparticles during preparation steps are considered undesirable species for the oxygen reduction reaction due to decreasing electrochemical active sites. However, we found that a small amount of oleylamine modified platinum nanoparticles showed significant enhancement of the electrochemical activity of the oxygen reduction reaction, even with the loss of the electrochemically active surface area. The enhancement was correlated with the downshift of the frontier d-band structure of platinum and the retardation of competitively adsorbed species. These results suggest that a capping organic molecule modified electrode can be a strategy to design an advanced electrocatalyst by modification of electronic structures

In Situ Transformation of Hydrogen-Evolving CoP Nanoparticles: Toward Efficient Oxygen Evolution Catalysts Bearing Dispersed Morphologies with Co-oxo/hydroxo Molecular Units

Reported herein is elucidation of a novel Co-based oxygen evolution catalyst generated in situ from cobalt phosphide (CoP) nanoparticles. The present CoP nanoparticles, efficient alkaline hydrogen-evolving materials at the cathode, are revealed to experience unique metamorphosis upon anodic potential cycling in an alkaline electrolyte, engendering efficient and robust catalytic environments toward the oxygen evolution reaction (OER). Our extensive ex situ characterization shows that the transformed catalyst bears porous and nanoweb-like dispersed morphologies along with unique microscopic environments mainly consisting of discrete cobalt-oxo/hydroxo molecular units within a phosphate-enriched amorphous network. Outstanding OER efficiency is achievable with the activated catalyst, which is favorably comparable to even a precious iridium catalyst. A more remarkable feature is its outstanding long-term stability, superior to iridium and conventional cobalt oxide-based materials. Twelve-hour bulk electrolysis continuously operating at high current density is completely tolerable with the present catalyst

Origin of the Enhanced Electrocatalysis for Thermally Controlled Nanostructure of Bimetallic Nanoparticles

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

High-Performance Hybrid Catalyst with Selectively Functionalized Carbon by Temperature-Directed Switchable Polymer

Carbon-supported Pt (Pt/C) catalyst was selectively functionalized with thermally responsive poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) to improve water transport in the cathode of proton exchange membrane fuel cell (PEMFC). Amine-terminated PNIPAM selectively reacted with the functional group of −COOH on carbon surfaces of Pt/C via the amide reaction by 1-ethyl-3-(3-dimethylaminopropyl)­carbodiimide (EDC) as a catalyst. Pt surfaces of Pt/C were intact throughout the carbon surface functionalization, and the carbon surface property could be thermally changed. The PNIPAM-functionalized Pt/C was well-dispersed, because of its hydrophilic surface property at room temperature during the catalyst ink preparation. In sharp contrast, when PEMFC was operated at 70 °C, PNIPAM-coated carbon surface of Pt/C became hydrophobic, which resulted in a decrease in water flooding in the cathode electrode. Because of the switched wetting property of the carbon surface, PEMFC with PNIPAM-functionalized Pt/C catalyst in the cathode showed high performance in the high current density region. To explain the enhanced water transport, we proposed a simple index as the ratio of systematic pressure (driving force) and retention force. The synthetic method presented here will provide a new insight into various energy device applications using organic and inorganic composite materials and functional polymers

Understanding Interface between Electrode and Electrolyte: Organic/Inorganic Hybrid Design for Fast Ion Conductivity

Ion transport is an important issue in electrochemical-based energy conversion and storage devices. Ion transport at the interface of the electrode and electrolyte is critical for performance. However, there is little understanding of the interface phenomena based on ion transport properties. Here, the proton transport behavior in a Nafion membrane (electrolyte) and that of an ionomer in the catalyst layer (electrode/electrolyte interface) was investigated simultaneously by electrochemical impedance spectroscopy. Our study indicates that the proton transport behavior in the catalyst layer is different from that in membrane. To elucidate the interface phenomena, we analyzed the Nafion electrolyte and proton behavior by molecular dynamics (MD). On the basis of the MD results, we modified the catalyst with a hybrid of inorganic Pt catalyst and organic 3-mercaptopropionic acid to promote a positive interfacial reaction between the electrolyte and electrode, which resulted in improved proton transport and performance