Developing efficient and inexpensive
electrocatalysts for the hydrogen
evolution reaction (HER) in alkaline water electrolysis plays a key
role for renewable hydrogen energy technology. The slow reaction kinetics
of HER in alkaline solutions, however, has hampered advances in high-performance
hydrogen production. Herein, we investigated the trends in HER activity
with respect to the binding energies of Ni-based thin film catalysts
by incorporating a series of oxophilic transition metal atoms. It
was found that the doping of oxophilic atoms enables the modulation
of binding abilities of hydrogen and hydroxyl ions on the Ni surfaces,
leading to the first establishment of a volcano relation between OH-binding
energies and alkaline HER activities. In particular, Cr-incorporated
Ni catalyst shows optimized OH-binding as well as H-binding energies
for facilitating water dissociation and improving HER activity in
alkaline media. Further enhancement of catalytic performance was achieved
by introducing an array of three-dimensional (3D) Ni nanohelixes (NHs)
that provide abundant surface active sites and effective channels
for charge transfer and mass transport. The Cr dopants incorporated
into the Ni NHs accelerate the dissociative adsorption process of
water, resulting in remarkably enhanced catalytic activities in alkaline
medium. Our approach can provide a rational design strategy and experimental
methodology toward efficient bimetallic electrocatalysts for alkaline
HER using earth-abundant elements.
The redox center of transition metal oxides and hydroxides is generally considered to be the metal site. Interestingly, proton and oxygen in the lattice recently are found to be actively involved in the catalytic reactions, and critically determine the reactivity. Herein, taking glycerol electrooxidation reaction as the model reaction, we reveal systematically the impact of proton and oxygen anion (de)intercalation processes on the elementary steps. Combining density functional theory calculations and advanced spectroscopy techniques, we find that doping Co into Ni-hydroxide promotes the deintercalation of proton and oxygen anion from the catalyst surface. The oxygen vacancies formed in NiCo hydroxide during glycerol electrooxidation reaction increase d-band filling on Co sites, facilitating the charge transfer from catalyst surface to cleaved molecules during the 2nd C-C bond cleavage. Consequently, NiCo hydroxide exhibits enhanced glycerol electrooxidation activity, with a current density of 100 mA/cm2 at 1.35 V and a formate selectivity of 94.3%.
Hydroxyapatite (HAP) is a green catalyst that has a wide range of applications in catalysis due to its high flexibility and multifunctionality. These properties allow HAP to accommodate a large number of catalyst modifications that can selectively improve the catalytic performance in target reactions. To date, many studies have been conducted to elucidate the effect of HAP modification on the catalytic activities for various reactions. However, systematic design strategies for HAP catalysts are not established yet due to an incomplete understanding of underlying structure–activity relationships. In this review, tuning methods of HAP for improving the catalytic performance are discussed: 1) ionic composition change, 2) morphology control, 3) incorporation of other metal species, and 4) catalytic support engineering. Detailed mechanisms and effects of structural modulations on the catalytic performances for attaining the design insights of HAP catalysts are investigated. In addition, computational studies to understand catalytic reactions on HAP materials are also introduced. Finally, important areas for future research are highlighted.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.