Electrochemical water splitting is a clean technology that can store the intermittent renewable wind and solar energy in H2 fuels. However, large-scale H2 production is greatly hindered by the sluggish oxygen evolution reaction (OER) kinetics at the anode of a water electrolyzer. Although many OER electrocatalysts have been developed to negotiate this difficult reaction, substantial progresses in the design of cheap, robust, and efficient catalysts are still required and have been considered a huge challenge. Herein, we report the simple synthesis and use of α-Ni(OH)2 nanocrystals as a remarkably active and stable OER catalyst in alkaline media. We found the highly nanostructured α-Ni(OH)2 catalyst afforded a current density of 10 mA cm(-2) at a small overpotential of a mere 0.331 V and a small Tafel slope of ~42 mV/decade, comparing favorably with the state-of-the-art RuO2 catalyst. This α-Ni(OH)2 catalyst also presents outstanding durability under harsh OER cycling conditions, and its stability is much better than that of RuO2. Additionally, by comparing the performance of α-Ni(OH)2 with two kinds of β-Ni(OH)2, all synthesized in the same system, we experimentally demonstrate that α-Ni(OH)2 effects more efficient OER catalysis. These results suggest the possibility for the development of effective and robust OER electrocatalysts by using cheap and easily prepared α-Ni(OH)2 to replace the expensive commercial catalysts such as RuO2 or IrO2.

The hydrogen oxidation/evolution reactions are two of the most fundamental reactions in distributed renewable electrochemical energy conversion and storage systems. The identification of the reaction descriptor is therefore of critical importance for the rational catalyst design and development. Here we report the correlation between hydrogen oxidation/evolution activity and experimentally measured hydrogen binding energy for polycrystalline platinum examined in several buffer solutions in a wide range of electrolyte pH from 0 to 13. The hydrogen oxidation/evolution activity obtained using the rotating disk electrode method is found to decrease with the pH, while the hydrogen binding energy, obtained from cyclic voltammograms, linearly increases with the pH. Correlating the hydrogen oxidation/evolution activity to the hydrogen binding energy renders a monotonic decreasing hydrogen oxidation/evolution activity with the hydrogen binding energy, strongly supporting the hypothesis that hydrogen binding energy is the sole reaction descriptor for the hydrogen oxidation/evolution activity on monometallic platinum.

The slow reaction kinetics of the hydrogen evolution and oxidation reactions (HER/HOR) on platinum in alkaline electrolytes hinders the development of alkaline electrolysers, solar hydrogen cells and alkaline fuel cells. A fundamental understanding of the exchange current density of the HER/HOR in alkaline media is critical for the search and design of highly active electrocatalysts. By studying the HER on a series of monometallic surfaces, we demonstrate that the HER exchange current density in alkaline solutions can be correlated with the calculated hydrogen binding energy (HBE) on the metal surfaces via a volcano type of relationship. The HER activity varies by several orders of magnitude from Pt at the peak of the plot to W and Au located on the bottom of each side of the plot, similar to the observation in acids. Such a correlation suggests that the HBE can be used as a descriptor for identifying electrocatalysts for HER/HOR in alkaline media, and that the HER exchange current density can be tuned by modifying the surface chemical properties.

Staying power: A new class of cathode catalysts based on supportless Pt (see picture, left) and PtPd nanotubes (NTs) is introduced. These materials have remarkable durability (right; CV=cyclic voltammetry, ECSA=electrochemical surface area) and high catalytic activity. They have the potential to circumvent most of the degradation pathways of current Pt/C and Pt‐black catalysts.

Much effort has been devoted in the development of efficient catalysts for electrochemical reduction of CO. Molecular level understanding of electrode-mediated process, particularly the role of bicarbonate in increasing CO reduction rates, is still lacking due to the difficulty of directly probing the electrochemical interface. We developed a protocol to observe normally invisible reaction intermediates with a surface enhanced spectroscopy by applying square-wave potential profiles. Further, we demonstrate that bicarbonate, through equilibrium exchange with dissolved CO, rather than the supplied CO, is the primary source of carbon in the CO formed at the Au electrode by a combination of in situ spectroscopic, isotopic labeling, and mass spectroscopic investigations. We propose that bicarbonate enhances the rate of CO production on Au by increasing the effective concentration of dissolved CO near the electrode surface through rapid equilibrium between bicarbonate and dissolved CO.

Understanding how pH affects the activity of hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is key to developing active, stable, and affordable HOR/HER catalysts for hydroxide exchange membrane fuel cells and electrolyzers. A common linear correlation between hydrogen binding energy (HBE) and pH is observed for four supported platinum-group metal catalysts (Pt/C, Ir/C, Pd/C, and Rh/C) over a broad pH range (0 to 13), suggesting that the pH dependence of HBE is metal-independent. A universal correlation between exchange current density and HBE is also observed on the four metals, indicating that they may share the same elementary steps and rate-determining steps and that the HBE is the dominant descriptor for HOR/HER activities. The onset potential of CO stripping on the four metals decreases with pH, indicating a stronger OH adsorption, which provides evidence against the promoting effect of adsorbed OH on HOR/HER.

Three-dimensional porous crystalline polyimide covalent organic frameworks (termed PI-COFs) have been synthesized. These PI-COFs feature non- or interpenetrated structures that can be obtained by choosing tetrahedral building units of different sizes. Both PI-COFs show high thermal stability (>450 °C) and surface area (up to 2403 m(2) g(-1)). They also show high loading and good release control for drug delivery applications.

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