Electrocatalytic recycling of waste nitrate (NO3−) to valuable ammonia (NH3) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH3 synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO3−-to-NH3 conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell Cu/CuOx and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner Cu/CuOx phases preferentially catalyze NO3− reduction to NO2−, which is rapidly reduced to NH3 at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO3−-to-NH3 Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO3− concentrations at pH 13, a high NH3 yield rate of 1.17 mmol cm−2 h−1 in 0.1 M NO3− at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports.
Co3O4 nanocubes are evaluated concerning their intrinsic electrocatalytic activity towards the oxygen evolution reaction (OER) by means of single‐entity electrochemistry. Scanning electrochemical cell microscopy (SECCM) provides data on the electrocatalytic OER activity from several individual measurement areas covering one Co3O4 nanocube of a comparatively high number of individual particles with sufficient statistical reproducibility. Single‐particle‐on‐nanoelectrode measurements of Co3O4 nanocubes provide an accelerated stress test at highly alkaline conditions with current densities of up to 5.5 A cm−2, and allows to derive TOF values of up to 2.8×104 s−1 at 1.92 V vs. RHE for surface Co atoms of a single cubic nanoparticle. Obtaining such high current densities combined with identical‐location transmission electron microscopy allows monitoring the formation of an oxy(hydroxide) surface layer during electrocatalysis. Combining two independent single‐entity electrochemistry techniques provides the basis for elucidating structure–activity relations of single electrocatalyst nanoparticles with well‐defined surface structure.
Complex solid solutions (“high entropy alloys” with a single solid‐solution phase) hold great promise in electrocatalysis because of their nearly unlimited number of different active sites exposed at the surface. It has been shown by theoretical studies that multiple arrangements of different elements directly neighboring a binding site create millions of differently active catalytic sites. We report a zooming‐in approach using scanning electrochemical cell microscopy (SECCM) to distinguish between the averaged electrochemical response of multiple active sites and active site‐specific electrochemical response. Using a thin film complex solid solution electrocatalyst and a range of SECCM single barrel capillaries with diameters from 1.2 µm to 50 nm, we observed an averaged electrochemical response for the oxygen reduction reaction with minor statistical variations for the larger capillary diameters. In contrast, significant statistical heterogeneity among the measured spots is observed for small capillary diameters. This statistical heterogeneity is attributed to the ability of the smaller probe size to address a comparatively smaller number of active sites with high or low activity dominating the measured electrocatalytic currents.
Coupling electrochemical generation of hydrogen with the concomitant formation of an industrially valuable product at the anode instead of oxygen can balance the high costs usually associated with water electrolysis. We report the synthesis of a variety of nanoparticulate LaCo1−xFexO3 perovskite materials through a specifically optimized spray‐flame nanoparticle synthesis method, using different ratios of La, Co, and Fe precursor compounds. Structural characterization of the resulting materials by XRD, TEM, FTIR, and XPS analysis revealed the formation of mainly perovskite‐type materials. The electrocatalytic performance of the formed perovskite‐type materials towards the oxygen evolution reaction and the ethanol oxidation reaction was investigated by using rotating disk electrode voltammetry. An increased Fe content in the precursor mixture leads to a decrease in the electrocatalytic activity of the nanoparticles. The selectivity towards alcohol oxidation in alkaline media was assessed by using the ethanol oxidation reaction as a model reaction. Operando electrochemistry/ATR‐IR spectroscopy results reveal that acetate and acetaldehyde are the final products, depending on the catalyst composition as well as on the applied potential.
We illustrate an all solid-state ZnÀair battery by utilizing the ability of a titanium-nitride-functionalized molecular catalyst to mediate the oxygen reduction reaction by avoiding the parasitic corrosion chemistry and the hydroxide-holding capacity of the Zirfon membrane. The efficient ionic communication between the half-cell electrodes provided by the Zirfon membrane in combination with the chemical/electrochemical stability of the TiN-based air electrode ultimately led to an all solid-state and air-breathing battery possessing high durability and stability.Electrochemical energy storage and conversion devices such as batteries, fuel cells and supercapacitors have the potential to address global warming and alarming pollution due to their near zero emission power output. [1][2][3][4][5][6][7] MetalÀair batteries are new generation batteries which are anticipated to contribute to long driving range per charge compared to conventional metal ion batteries. [8][9][10][11][12] The air electrode architecture is expected to increase gravimetric energy storage capability of the device since oxygen in principle can be accessed from atmosphere circumventing the storage of oxidant on board the device. [13][14][15] Though non aqueous Li air batteries are being pursued intensely across the world, aqueous ZnÀair batteries are much evolved and even used in commercial hearing aid devices. [16][17][18][19][20][21][22][23][24] However, oxygen reduction reaction (ORR), the cathodic halfcell reaction in air batteries often require precious metal based electrocatalyst to catalyze the 4 electron scission of molecular oxygen. [25][26][27][28][29] Usually Pt is supported on carbon which is known to undergo extensive corrosion in presence of oxygen and especially peroxide, the 2 electron product of ORR. [30][31][32] Pt is also known to catalyze carbon corrosion resulting in sintering and agglomeration of Pt nanoparticles and ultimately to the loss of precious metals. [33,34] We demonstrate that by replacing carbon with conducting titanium nitride (TiN), an extremely corrosion resistant as well as chemically stable material used in aberration industry, [35][36][37] carbon corrosion and its negative consequences can be addressed at the air electrode of metalair batteries. Further, we show a strategy for tuning the catalytic activity of this promising corrosion resistant catalytic support by simple diazotization reaction. [38] We have exploited the base reservoir capability of Zirfon PERL UTP 500 membrane for ionic communication between the half-cells. [39,40] To develop an all solid-state metalÀair battery. The results demonstrate that TiN based catalytic system outperforms carbon based catalysts in terms of long-term stability and durability ultimately leading to an all solid-state ZnÀair battery possessing a corrosion resistant air electrode.TiN particles were flake like with irregular morphology, scanning electron microscopic image, Figure 1a. Energy dispersive X-ray (EDX), Figure 1b, clearly indicates the constituent elements are m...
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