A method to count the number of electrons accumulated in carbon nitride green radicals using a methylviologen redox indicator is reported.

An itrogen-stabilized single-atom catalyst containing low-valence zinc atoms (Zn d+ -NC) is reported. It contains saturated four-coordinate (Zn-N 4 )a nd unsaturated threecoordinate (Zn-N 3 )s ites.T he latter makes Zn al ow-valence state,a sdeduced from X-ray photoelectron spectroscopy, Xray absorption spectroscopy, electron paramagnetic resonance, and density functional theory.Z n d+ -NC catalyzese lectrochemical reduction of CO 2 to CO with near-unity selectivity in water at an overpotential as lowa s3 10 mV.Acurrent density up to 1Acm À2 can be achieved together with high CO selectivity of > 95 %using Zn d+ -NC in aflowcell. Calculations suggest that the unsaturated Zn-N 3 could dramatically reduce the energy barrier by stabilizing the COOH* intermediate owingtothe electron-rich environment of Zn. This work sheds light on the relationship among coordination number,valence state,a nd catalytic performance and achieves high current densities relevant for industrial applications.

Recently, a large number of nanostructured metal-containing materials have been developed for the electrochemical CO 2 reduction reaction (eCO 2 RR). However, it remains a challenge to achieve high activity and selectivity with respect to the metal load due to the limited concentration of surface metal atoms. Here, it is reported that the bismuth-based metal-organic framework Bi(1,3,5-tris(4-carboxyphenyl)benzene), herein denoted Bi(btb), works as a precatalyst and undergoes a structural rearrangement at reducing potentials to form highly active and selective catalytic Bi-based nanoparticles dispersed in a porous organic matrix. The structural change is investigated by electron microscopy, X-ray diffraction, total scattering, and spectroscopic techniques. Due to the periodic arrangement of Bi cations in highly porous Bi(btb), the in situ formed Bi nanoparticles are well-dispersed and hence highly exposed for surface catalytic reactions. As a result, high selectivity over a broad potential range in the eCO 2 RR toward formate production with a Faradaic efficiency up to 95(3)% is achieved. Moreover, a large current density with respect to the Bi load, i.e., a mass activity, up to 261(13) A g −1 is achieved, thereby outperforming most other nanostructured Bi materials.

Fourier transform infrared−attenuated total reflectance (FTIR-ATR) spectroscopy was used to study in detail water vapor sorption in a short-side-chain perfluorosulfonic acid ionomer membrane suitable for use as electrolyte in proton exchange membranes fuel cells. The analysis of the membrane IR spectra, at different values of relative humidity (0.00−0.50) and at 35 °C, allows to identify four types of water molecules, characterized by decreasing strength of interaction with the polymer sulfonate groups. The actual concentration of the different water species inside the membrane was determined by calibrating the IR absorbance data with independent measurements of total water vapor uptake. The sorption of the different populations of water can be represented by Langmuir isotherms: the first population is directly attached to sulfonate sites, while the others form subsequent layers, adsorbed one onto the other in a shell-like structure. To describe the overall sorption behavior of the different populations, four adjustable parameters are required, which are consistent with literature data, thus supporting the validity of the physical model considered.

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