A promising family of mixed transition-metal oxides (MTMOs) (designated as Ax B3-x O4 ; A, B=Co, Ni, Zn, Mn, Fe, etc.) with stoichiometric or even non-stoichiometric compositions, typically in a spinel structure, has recently attracted increasing research interest worldwide. Benefiting from their remarkable electrochemical properties, these MTMOs will play significant roles for low-cost and environmentally friendly energy storage/conversion technologies. In this Review, we summarize recent research advances in the rational design and efficient synthesis of MTMOs with controlled shapes, sizes, compositions, and micro-/nanostructures, along with their applications as electrode materials for lithium-ion batteries and electrochemical capacitors, and efficient electrocatalysts for the oxygen reduction reaction in metal-air batteries and fuel cells. Some future trends and prospects to further develop advanced MTMOs for next-generation electrochemical energy storage/conversion systems are also presented.

Mixed transition-metal oxides: design, synthesis, and energy-related applications.

Surface science studies of model fuel cell electrocatalysts

Interfacial processes involving electrocatalytic evolution and oxidation of H2, and the role of chemisorbed H

Hydrogen produced from water and renewable energy could fuel a large fleet of proton-exchange-fuel-cell vehicles in the future. However, the dependence on expensive Pt-based electrocatalysts in such fuel cells remains a major obstacle for a widespread deployment of this technology. One solution to overcome this predicament is to reduce the Pt content by a factor of ten by replacing the Pt-based catalysts with non-precious metal catalysts at the oxygen-reducing cathode. Fe- and Co-based electrocatalysts for this reaction have been studied for over 50 years, but they were insufficiently active for the high efficiency and power density needed for transportation fuel cells. Recently, several breakthroughs occurred that have increased the activity and durability of non-precious metal catalysts (NPMCs), which can now be regarded as potential competitors to Pt-based catalysts. This review focuses on the new synthesis methods that have led to these breakthroughs. A modeling analysis is also conducted to analyze the improvements required from NPMC-based cathodes to match the performance of Pt-based cathodes, even at high current density. While no further breakthrough in volume-specific activity of NPMCs is required, incremental improvements of the volume-specific activity and effective protonic conductivity within the fuel-cell cathode are necessary. Regarding durability, NPMCs with the best combination of durability and activity result in ca. 3 times lower fuel cell performance than the most active NPMCs at 0.80 V. Thus, major tasks will be to combine durability with higher activity, and also improve durability at cell voltages greater than 0.60 V.

Recent advances in non-precious metal catalysis for oxygen-reduction reaction in polymer electrolyte fuel cells

The kinetics of the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) on polycrystalline platinum [Pt(pc)] and high surface area carbon-supported platinum nanoparticles (Pt/C) were studied in 0.1 M KOH using rotating disk electrode (RDE) measurements. After corrections of noncompensated solution resistance from ac impedance spectroscopy and of hydrogen mass transport in the HOR branch, the kinetic current densities were fitted to the Butler-Volmer equation using a transfer coefficient of α = 0.5, from which HOR/HER exchange current densities on Pt(pc) and Pt/C were obtained, and the HOR/HER mechanisms in alkaline solution were discussed. Unlike the HOR/HER rates on Pt electrodes in alkaline solution, the HOR/HER rates on a Pt electrode in 0.1 M HClO 4 were limited entirely by hydrogen diffusion, which renders the quantification of the HOR/HER kinetics impossible by conventional RDE measurements. The simulation of the hydrogen anode performance based on the specific exchange current densities of the HOR/HER at 80°C illustrates that in addition to the oxygen reduction reaction cell voltage loss on the cathode, the slow HOR kinetics are projected to cause significant anode potential losses in alkaline fuel cells for low platinum loadings (> 130 mV at 0.05 Mg pt /CM 2 anode and 1.5 A/cm 2 anode ), contrary to what is reported for proton exchange membrane fuel cells.

/pdf/hydrogen-oxidation-and-evolution-reaction-kinetics-on-yxboc1tqjr.pdf

V.S. Bagotzky

Papers

Mechanism of electro-oxidation of methanol on the platinum electrode☆

Generalized scheme of chemisorption, electrooxidation and electroreduction of simple organic compounds on platinum group metals

Electrocatalysis of the oxygen reduction process on metal chelates in acid electrolyte

Absorption of organic substances on platinum electrodes

Adsorption of anions on smooth platinum electrodes