Photoelectroreduction of Building-Block Chemicals.

Conventional photoelectrochemical cells utilize solar energy to drive the chemical conversion of water or CO2 into useful chemical fuels. Such processes are confronted with general challenges, including the low intrinsic activities and inconvenient storage and transportation of their gaseous products. A photoelectrochemical approach is proposed to drive the reductive production of industrial building-block chemicals and demonstrate that succinic acid and glyoxylic acid can be readily synthesized on Si nanowire array photocathodes free of any cocatalyst and at room temperature. These photocathodes exhibit a positive onset potential, large saturation photocurrent density, high reaction selectivity, and excellent operation durability. They capitalize on the large photovoltage generated from the semiconductor/electrolyte junction to partially offset the required external bias, and thereby make this photoelectrosynthetic approach significantly more sustainable compared to traditional electrosynthesis.

Mo2C Nanoparticles Dispersed on Hierarchical Carbon Microflowers for Efficient Electrocatalytic Hydrogen Evolution.

The development of nonprecious metal based electrocatalysts for hydrogen evolution reaction (HER) has received increasing attention over recent years. Previous studies have established Mo2C as a promising candidate. Nevertheless, its preparation requires high reaction temperature, which more than often causes particle sintering and results in low surface areas. In this study, we show supporting Mo2C nanoparticles on the three-dimensional scaffold as a possible solution to this challenge and develop a facile two-step preparation method for ∼3 nm Mo2C nanoparticles uniformly dispersed on carbon microflowers (Mo2C/NCF) via the self-polymerization of dopamine. The resulting hybrid material possesses large surface areas and a fully open and accessible structure with hierarchical order at different levels. MoO42- was found to play an important role in inducing the formation of this morphology presumably via its strong chelating interaction with the catechol groups of dopamine. Our electrochemical evaluation demonstrates that Mo2C/NCF exhibits excellent HER electrocatalytic performance with low onset overpotentials, small Tafel slopes, and excellent cycling stability in both acidic and alkaline solutions.

Efficient Photoelectrochemical Hydrogen Evolution on Silicon Photocathodes Interfaced with Nanostructured NiP2 Cocatalyst Films.

Increasing attention has now been focused on the photoelectrochemical (PEC) hydrogen evolution as a promising route to transforming solar energy into chemical fuels. Silicon is one of the most studied PEC electrode materials, but its performance is still limited by its inherent PEC instability and electrochemical inertness toward water splitting. To achieve significant PEC activities, silicon-based photoelectrodes usually have to be coupled with proper cocatalysts, and thus, the formed semiconductor-cocatalyst interface presents a critical structural parameter in the rational design of efficient PEC devices. In this study, we directly grow nanostructured pyrite-phase nickel phosphide (NiP2) cocatalyst films on textured pn+-Si photocathodes via on-surface reaction at high temperatures. The areal loading of the cocatalyst film can be tailored to achieve an optimal balance between its optical transparency and electrocatalytic activity. As a result, our pn+-Si/Ti/NiP2 photocathodes demonstrate a great PEC onset potential of 0.41 V versus reversible hydrogen electrode (RHE), a decent photocurrent density of ∼12 mA/cm2 at the thermodynamic potential of hydrogen evolution, and an impressive operation durability for at least 6 h in 0.5 M H2SO4. Comparable PEC performance is also observed in 1 M potassium borate buffer (pH = 9.5) using this device.

Cobalt hexacyanoferrate nanoparticles as a high-rate and ultra-stable supercapacitor electrode material.

Although great recent efforts have been invested to improve the performance of supercapacitors, these energy storage devices still fall short of meeting our expectations because of their limited working voltage, insufficient cycle life, and high manufacturing cost. Here, we report the facile preparation of cobalt hexacyanoferrate (CoHCFe) nanoparticles, which have an analogous structure to Prussian blue but with many vacant ferricyanide sites. In 0.5 M Na2SO4, CoHCFe exhibits specific capacitance of >250 F/g, excellent rate capability, and ultrahigh cycling stability with capacitance retention of 93.5% after 5000 cycles. Furthermore, CoHCFe was paired up with a carbon black modified graphene (mRGO) negative electrode to form asymmetric supercapacitors. They deliver a wide working voltage of ∼2.4 V in Na2SO4, large energy density and power density. Given its high electrochemical performance, chemical robustness, environmental benignity, ease of preparation and low cost, CoHCFe as well as other Prussian blue analogues clearly deserve more attention for future energy storage applications.