Identification of catalytically active sites at solid/liquid interfaces under reaction conditions is an essential task to improve the catalyst design for sustainable energy devices. Electrochemical scanning tunneling microscopy (EC‐STM) combines the control of the surface reactions with imaging on a nanoscale. When performing EC‐STM under reaction conditions, the recorded analytical signal shows higher fluctuations (noise) at active sites compared to non‐active sites (noise‐EC‐STM or n‐EC‐STM). In the past, this approach has been proven as a valid tool to identify the location of active sites. In this work, the authors show that this method can be extended to obtain quantitative information of the local activity. For the platinum(111) surface under oxygen reduction reaction conditions, a linear relationship between the STM noise level and a measure of reactivity, the turn‐over frequency is found. Since it is known that the most active sites for this system are located at concave sites, the method has been applied to quantify the activity at steps. The obtained activity enhancement factors appeared to be in good agreement with the literature. Thus, n‐EC‐STM is a powerful method not only to in situ identify the location of active sites but also to determine and compare local reactivity.

Herein, we demonstrate an easy way to improve the hydrogen evolution reaction (HER) activity of Pt electrodes in alkaline media by introducing Ni–Fe clusters. As a result, the overpotential needed to achieve a current density of 10 mA cm−2 in H2‐saturated 0.1 m KOH is reduced for the model single‐crystal electrodes down to about 70 mV. To our knowledge, these modified electrodes outperform any other reported electrocatalysts tested under similar conditions. Moreover, the influence of 1) Ni to Fe ratio, 2) cluster coverage, and 3) the nature of the alkali‐metal cations present in the electrolyte on the HER activity has been investigated. The observed catalytic performance likely originates from both the improved water dissociation at the Ni–Fe clusters and the subsequent optimal hydrogen adsorption and recombination at Pt atoms present at the Ni–Fe/Pt boundary.

Materials derived from surface‐mounted metal–organic frameworks (SURMOFs) are promising electrocatalysts for the oxygen evolution reaction (OER). A series of mixed‐metal, heterostructured SURMOFs is fabricated by the facile layer‐by‐layer deposition method. The obtained materials reveal record‐high electrocatalyst mass activities of ≈2.90 kA g−1 at an overpotential of 300 mV in 0.1 m KOH, superior to the benchmarking precious and nonprecious metal electrocatalysts. This property is assigned to the particular in situ self‐reconstruction and self‐activation of the SURMOFs during the immersion and the electrochemical treatment in alkaline aqueous electrolytes, which allows for the generation of NiFe (oxy)hydroxide electrocatalyst materials of specific morphology and microstructure.

Results from Pt model catalyst surfaces have demonstrated that surface defects, in particular surface concavities, can improve the oxygen reduction reaction (ORR) kinetics. It is, however, a challenging task to synthesize nanostructured catalysts with such defective surfaces. Hence, we present a one-step and up-scalable top-down approach to produce Pt/C catalyst (with ~3 nm Pt nanoparticle diameter). Using high-resolution transmission electron microscopy and tomography, electrochemical techniques, high energy X-ray measurements and positron annihilation spectroscopy, we provide evidence of a high density of surface defects (including surface concavities). The ORR activity of the developed catalyst exceeds that of commercial Pt/C catalyst, at least 2.7-times in terms of specific (~1.62 mA/cm 2 Pt at 0.9 V vs the reversible hydrogen electrode) and at least 1.7-times in terms of mass activity (~712 mA/mg Pt), which can be correlated to the enhanced amount of surface defects. Besides, the technique used here reduces the Page 2 of 51 ACS Paragon Plus Environment ACS Catalysis 3 complexity of the synthesis (and therefore production costs) compared to state-of-the-art bottom-up techniques. This information is available free of charge on the ACS Publications website. Coincident Doppler broadening spectrum, WAXS measurements, Rietveld refinement data, Reference ORR polarization curve, Accelerated durability test, TEM analysis AUTHOR INFORMATION

Revealing the nature of active sites on Pt-Gd and Pt-Pr alloys during the oxygen reduction reaction // ACS Applied Materials and Interfaces 14 (2022) 19604-19613.