Electrocatalytic hydrogen peroxide (H2O2) production via the two-electron oxygen reduction reaction is a promising alternative to the energy-intensive and high-pollution anthraquinone oxidation process. However, developing advanced electrocatalysts with high H2O2 yield, selectivity, and durability is still challenging, because of the limited quantity and easy passivation of active sites on typical metal-containing catalysts, especially for the state-of-the-art single-atom ones. To address this, we report a graphene/mesoporous carbon composite for high-rate and high-efficiency 2e− oxygen reduction catalysis. The coordination of pyrrolic-N sites -modulates the adsorption configuration of the *OOH species to provide a kinetically favorable pathway for H2O2 production. Consequently, the H2O2 yield approaches 30 mol g−1 h−1 with a Faradaic efficiency of 80% and excellent durability, yielding a high H2O2 concentration of 7.2 g L−1. This strategy of manipulating the adsorption configuration of reactants with multiple non-metal active sites provides a strategy to design efficient and durable metal-free electrocatalyst for 2e− oxygen reduction.
An ultralight silica aerogel is among the most versatile materials available for technical applications; however, it remains a huge challenge to reduce its manufacturing cost. Here, we report on a simple approach for the preparation of silica foam monoliths with ultrahigh porosity up to 99.5% and specific surface area as high as 755 m g, which are similar to those of an aerogel. Our strategy is based on the effective stabilization of water-in-oil high internal phase emulsions by a hydrophobic silica precursor polymer, hyperbranched polyethoxysiloxane because of its hydrolysis-induced amphiphilicity. After conversion of this precursor polymer to silica, the emulsions are solidified without significant volume shrinkage. Thus, mechanically strong macroporous silica monoliths are obtained after removal of its liquid components. According to nitrogen sorption data, the resulting silica foams exhibit a high specific surface area and a foam skeleton consisting of both micropores (<2 nm) and mesopores (2-50 nm). The pore size, porosity, and surface area can be regulated by varying pH as well as the concentration of the silica precursor in the oil phase. In addition, the pore size can be adjusted by controlling shear force during emulsification. This work opens a new avenue for producing ultralight porous materials amenable to numerous applications.
Polymeric carbon nitride photocatalyst has attracted much attention due to its visible light response and high chemical stability. However, bulk carbon nitride has a wide band gap and low polymerization, limiting its photocatalytic performance for water splitting. Synthesizing highly polymerized carbon nitride with a narrow band gap still remains challenging. Herein, we propose an ionothermal protocol using supramolecular precursors to fabricate highly polymerized wine-red carbon nitride (WRCN) nanosheets. Both theoretical and experimental investigations revealed that the supramolecular precursor with a high C:N ratio leads to an upward shift of the valence band edge, while the ionothermal synthesis promotes a high polymerization degree, leading to a narrow band gap of 1.82 eV for WRCN. Benefiting from enhanced light absorption and charge separation efficiency, WRCN-loaded hematite photoanode exhibits a much higher photocurrent density than both pristine hematite and bulk carbon nitride decorated hematite. This work may provide a novel strategy to manipulate the electronic structures of carbon nitrides for enhanced photoelectrochemical performances.
Function
convergence of gas sensing and neuromorphic computing
is attracting much research attention due to the promising potential
in electronic olfactory, artificial intelligence, and internet of
everything systems. However, the current neuromorphic gas-sensing
systems are either realized via integration of gas detectors and neuromorphic
devices or operating with three-terminal synaptic transistors at high
voltages, leading to a rather high system complexity or power consumption.
Herein, gas-modulated synaptic diodes with lateral structures are
developed to converge sensing, processing, and storage functions into
a single device. The lateral synaptic diode is based on a p–n
junction of an organic semiconductor (OSC) and amorphous In-Ga-Zn-O,
in which the upper OSC layer can directly interact with the gas molecules
in the atmosphere. Typical synaptic behaviors triggered by ammonia,
including inhibitory postsynaptic current and paired-pulse depression,
are successfully demonstrated. Meanwhile, a low power consumption
of 6.3 pJ per synaptic event has been achieved, which benefits from
the simple device structure, the decent chemosensitivity of the OSC,
and the low operation voltage. A simulated ammonia analysis in human
exhaled breath is further conducted to explore the practical application
of the synaptic diode. Therefore, this work provides a gas-modulated
synaptic diode for circuit-compact and power-efficient artificial
olfactory systems.
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