A double-exchange interaction (DEI) was demonstrated to boost the oxygen evolution reaction (OER) in spinel oxides. DEI was ignited by synergistic actions of constructing nanoheterojunctions and creating oxygen vacancy (V O ) in spinel NiCo 2 O 4 . DEI between octahedrally coordinated Ni and Co resulted in the generation of superior OER active centers Co (3−δ)+ and Ni 3+ . The multiple synergistic effects empower the electrocatalyst with exceptional OER activity, with an overpotential of 270 ± 3 mV at 10 mA/cm 2 and a Tafel slope of 39 mV/dec, both of which are among the best values for NiCo 2 O 4 -based nanostructures, and even better than those for IrO 2 and RuO 2 . Communication pubs.acs.org/JACS

A class of Pd−Ni−P electrocatalysts are prepared for the ethanol electrooxidation reaction (EOR). Xray diffraction and transmission electron microscope reveal that the synthesized Pd−Ni−P catalyst possesses a more amorphous structure with smaller particle sizes when compared with a Pd−Ni sample without P and a control Pd black (Pd-blk) sample. The Pd−Ni−P catalyst contains double the number of electrocatalytically active sites (12.03%) compared with the Pd−Ni (6.04%) and Pd-blk (5.12%) samples. For the EOR, the Pd−Ni−P catalyst has the lowest onset potential (−0.88 V vs SCE), the most negative peak potential (−0.27 V vs SCE), and the highest EOR activity in 0.1 M KOH solution. Moreover, a 110 mV decrease in overpotential is observed for the EOR on the Pd−Ni−P catalyst compared with the Pd-blk catalyst. A Tafel slope of 60 mV/dec at low polarization potentials (<−0.76 V vs SCE) was obtained for EOR at a Pd−Ni−P-coated electrode with a reaction rate constant of 2.8 × 10 −4 cm•S −1 •M −1 at −0.3 V vs SCE in KOH media. Finally, we find that the electrooxidation of ethanol on the Pd−Ni−P catalyst undergoes a 4-electron process to acetate.

Multimetallic nanoclusters (MMNCs) offer unique and tailorable surface chemistries that hold great potential for numerous catalytic applications. The efficient exploration of this vast chemical space necessitates an accelerated discovery pipeline that supersedes traditional “trial-and-error” experimentation while guaranteeing uniform microstructures despite compositional complexity. Herein, we report the high-throughput synthesis of an extensive series of ultrafine and homogeneous alloy MMNCs, achieved by 1) a flexible compositional design by formulation in the precursor solution phase and 2) the ultrafast synthesis of alloy MMNCs using thermal shock heating (i.e., ∼1,650 K, ∼500 ms). This approach is remarkably facile and easily accessible compared to conventional vapor-phase deposition, and the particle size and structural uniformity enable comparative studies across compositionally different MMNCs. Rapid electrochemical screening is demonstrated by using a scanning droplet cell, enabling us to discover two promising electrocatalysts, which we subsequently validated using a rotating disk setup. This demonstrated high-throughput material discovery pipeline presents a paradigm for facile and accelerated exploration of MMNCs for a broad range of applications.

Focusing on methanol tolerance, a series of heat-treated metalloporphyrins were investigated by steady-state voltammetry with a rotating disk electrode. The heat-treated CoTPP/FeTPP (tetraphenylporphyrin) shows the optimum catalytic activity for oxygen reduction with an onset catalytic potential [0.9 V vs. reversible hydrogen electrode (RHE)] close to that of platinum black catalyst (1.0 V vs. RHE). However, the catalytic activity for oxygen reduction on platinum black catalyst is severely affected by the presence of 1.0 M methanol, resulting in a negative shift of the catalytic potential and a significant decrease in catalytic current. The catalytic activity for oxygen reduction on the heat-treated metalloporphyrin is not appreciably affected by the presence of the same amount of methanol in an acidic electrolytic solution. The catalytic activity of the heat-treated binary metalloporphyrin catalyst is better than that of only a heat-treated single metalloporphyrin. The best heat-treatment (HT) temperature for HT-CoTPP/FeTPP is 600ЊC. The catalytic kinetic process is analyzed using various polarization curves for oxygen reduction at different rotation rates. The slopes obtained from the Koutecky ´-Levich plots have verified that the heat-treated metalloporphyrins can catalyze a four-electron reduction of oxygen to water over a wide potential range.

Fuel (methanol) crossover through the polymeric electrolyte membrane in a single direct methanol fuel cell (DMFC) was determined by monitoring the amount of CO2 produced from methanol oxidation. Instead of measuring CO2 from only the cathode by a conventional method, the amounts of CO2 at both of the cathode and the anode were determined in the present study. Gravimetric determination of BaCO3 was employed to accurately analyze the amount of CO2. The equivalent current of methanol crossover can be calculated from the discharge current of the fuel cell and the sum of dry BaCO3 precipitate collected at the anode and the cathode exhausts. The common experimental deviation of measuring methanol crossover caused by CO2 permeation through polymeric electrolyte membrane can be corrected with the proposed method. These data of methanol crossover were compared with the data of single cell polarization behaviors at different methanol concentrations and different temperatures. The energy density of the DMFC is not only dependent on the cell discharge performance but also significantly dependent on the faradaic efficiency that is directly linked to methanol crossover. Under the optimized operating conditions, 1.0 M methanol at 60°C, the DMFC has an energy density of 1800 Wh/kg based on pure methanol. © 2003 The Electrochemical Society. All rights reserved.

Ru@RuO2 core‐shell nanorods were successfully synthesized by heat‐treating Ru nanorods with air oxidation through an accurate control of the temperature and time. The structure, composition, dimension, and adsorption property of the core‐shell nanorods were well characterized with XRD and TEM. The catalytic activity and stability were electrochemically evaluated with a rotating disk electrode, a rotating ring‐disk electrode, and chronopotentiometric methods. The Ru@RuO2 nanorods reveal excellent bifunctional catalytic activity and robust stability for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The overpotentials for OER and HER are 320 mV and 137 mV at the current density of 10 mA cm−2, respectively. The catalytic activity of Ru@RuO2 nanorods for OER is 6.5 times higher than that of the state‐of‐the‐art catalyst IrO2 according to the catalytic current density measured at 1.60 V (versus RHE). The catalytic activity of Ru@RuO2 nanorods for HER is comparable to 40% Pt/C by comparing the catalytic current densities at −0.2 V.

A plasma-enhanced chemical vapor deposition (PECVD) process using a CH 4 :H 2 gas mixture creates vertically aligned carbon nanowalls (CNWs) on glassy carbon (GC) and Si substrates. Metal catalysts are not required for the nucleation and growth of CNWs on the substrates. The PECVD deposition temperatures and reaction times alter the morphology and thickness of the resulting CNW layer. A low-pressure, post-processing N 2 :Ar plasma treatment dopes the CNWs with nitrogen, and X-ray photoelectron spectroscopy measurements demonstrate that nitrogen is present at 4-20 atomic% with varying CN x bonding configurations dependent upon processing conditions. Raman spectroscopy shows relatively high intensity disorder bands (I D ) compared to lower intensity graphitic bands (I G ) indicating small crystalline domains. Rotating disk electrode voltammetry results show that the number of electrons (n) and kinetic current density (j k ) of the oxygen reduction reaction both increase with nitrogen content. In addition, n and j k increase with thickness of the nitrogen-containing CNW deposit. The results indicate that nitrogen-doped CNWs have higher electrochemical reactivity than their non-doped counterparts.

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