Browsing by Subject "Nitrogen doping"

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Binder‐free N‐functionalized carbon electrodes for oxygen evolution reaction
(2023) Song, Feihong; Straten, Jan W.; Lin, Yang‐Ming; Ding, Yuxiao; Schlögl, Robert; Heumann, Saskia; Mechler, Anna K.
The oxygen evolution reaction (OER) is one of the bottlenecks of electrochemical water splitting. Metal‐free carbons from biomass are highly abundant and can be easily synthesized. Their low price, high conductivity and functionalization makes them promising materials. Herein, we report about free‐standing carbon electrodes as electrocatalysts for the OER. In contrast to powder‐based catalysts, free‐standing electrodes not only avoid additives, but also facilitate post analysis and better reflect industrial conditions. Here, the performance of pure carbon electrodes is compared to those of N‐functionalized ones. Utilizing several analytical techniques, the difference in performance can be rationalized by physical properties. Especially, the analysis of the gaseous products is shown to be of crucial importance. It reveals that N‐doped carbons generate more oxygen and are more robust against carbon corrosion. This illustrates the importance of measuring selectivity especially for carbon electrocatalysts, as higher currents do not necessarily result in higher catalytic activity.
A comparative study on the influence of N‐doped primary and secondary hydrochars on the electrochemical performance of biobased carbon electrodes for energy storage application
(2024) Straten, Jan Willem; Alhnidi, Muhammad‐Jamal; Mustaka, Erlir; Alchoumari, Ghassan; Jung, Dennis; Kruse, Andrea
The hydrothermal carbonization (HTC) technique and subsequent pyrolysis were applied. Herein, two different types of biobased feedstocks, sucrose (Suc) and Miscanthus (Mis), were chosen. Urea served as N precursor for the in situ doping. HTC of Suc and Mis with urea leads to N‐doped hydrochars (N‐HCs). Suc and Mis decompose in different, complex degradation pathways, which leads to the emergence of N‐HCs consisting of distinct ratios of N‐containing primary chars (N‐PCs) and secondary chars (N‐SCs). After pyrolysis, maximum N contents of 5.6 wt % and 4.8 wt % of the N‐doped pyrolyzed hydrochar (N‐PHC) electrodes from Suc and Mis, respectively were reached. The role of PC and SC formation on the impact of N‐doping in the context of physicochemical properties of the N‐PHCs was compared with each other. In this study, they were tested with respect to the influence of N‐PCs and N‐SCs on their electrochemical performance in energy storage application. It turned out that the electrical conductivity (EC) and specific capacitances increased. Highest EC value of 129.1 S ⋅ cm −1 was obtained with N‐PHC based on Suc. Simultaneously, enhanced average specific capacitances of 47.0 F ⋅ g −1 at 5 mV ⋅ s −1 and 3.5 F ⋅ g −1 at 100 mV ⋅ s −1 are ascertained with N‐PHCs from Suc and Mis, respectively.