Currently, hydrogen production is based on the reforming process, leading to the emission of pollutants; therefore, a substitute production method is imminently required. Water electrolysis is an ideal alternative for large-scale hydrogen production, as it does not produce any carbon-based pollutant byproducts. The production of green hydrogen from water electrolysis using intermittent sources (e.g., solar and eolic sources) would facilitate clean energy storage. However, the electrocatalysts currently required for water electrolysis are noble metals, making this potential option expensive and inaccessible for industrial applications. Therefore, there is a need to develop electrocatalysts based on earth-abundant and low-cost metals. Nickel-based electrocatalysts are a fitting alternative because they are economically accessible. Extensive research has focused on developing nickel-based electrocatalysts for hydrogen and oxygen evolution. Theoretical and experimental work have addressed the elucidation of these electrochemical processes and the role of heteroatoms, structure, and morphology. Even though some works tend to be contradictory, they have lit up the path for the development of efficient nickel-based electrocatalysts. For these reasons, a review of recent progress is presented herein.

The synthesis of hybrid platinum materials is fundamental to enable alkaline water electrolysis for cost-effective H 2 generation. In this work, we have used a galvanostatic method to codeposit PtNi films onto polycrystalline gold. The surface concentrations of Ni (Γ Ni ) and Pt (Γ Pt ) were calculated from electrochemical measurements; the Γ Pt /Γ Ni ratio and electrocatalytic activity of these materials towards hydrogen evolution reaction (HER) in 1 M KOH show a strong dependence on the current density pulse applied during the electrodeposition. Analysis of the Tafel parameters hints that, on these deposits, HER proceeds through a Volmer-Heyrovsky mechanism. The galvanostatically deposited PtNi layers present a high current output per Pt gram, 3199 A g Pt À 1 , which is significantly larger compared to other PtNi-based materials obtained by more extended and more complex synthesis methods.

The electroxidation of carbon monoxide has been used as a prototype reaction in fundamental electrocatalysis1. On Pt electrodes, the CO bulk electroxidation is a typical example of a bistable electrochemical system2. The bistable kinetics of the reaction stems from the interplay between the competitive Langmuir-Hinshelwood mechanism and the controlled mass transport of CO toward the electrode. On macroscopic Pt electrodes, different kinds of spatio-temporal instabilities may occur during the CO oxidation depending on the nature and the strength of coupling existing between different parts of the electrochemical system3,4. In this presentation we will discuss the influence of the size, the interelectrode distance and the supporting electrolyte concentration on the dynamic behaviour of a Pt microelectrode array in the electrooxidation of saturated CO solutions. A custom built galvanostat allows the individual currents flowing through each of the microelectrodes to be measured. Three different kinds of cooperative behaviour could be evidenced for the first time and explained with the help of mathematical modelling. When the applied reaction current value is linearly increased, sequential activation of the microelectrodes was observed (cf. Fig.), while a complex dynamical switching regime was obtained when the current was kept constant5. At low supporting electrolyte concentration, spontaneous oscillations of the potential emerged through the coupling of individual electrodes. Acknowledgements: Financial support from the International Center for Frontier Research in Chemistry (University of Strasbourg) and of the Labex “Chemistry of Complex Systems” is gratefully acknowledged F. Maillard, G.Q. Lu, A. Wieckowski, U. Stimming, J. Phys. Chem. B 109, 16230, 2005 M.T.M. Koper, T.J. Schmidt, N.M. Markovic, P.N. Ross, J. Phys. Chem. B 105, 8381, 2001 R. Morschl, J. Bolten, A. Bonnefont, K. Krischer, J. Phys. Chem. C, 112, 9548, 2008 P. Bauer, A. Bonnefont, K. Krischer, ChemPhysChem, 11, 3002, 2010 D. A. Crespo-Yapur, A. Bonnefont, R. Schuster, K. Krischer, E.R. Savinova, ChemPhysChem, 14, 1117, 2013