High-density Ag nanosheets for selective electrochemical CO2 reduction to CO.

To increase the specific surface area, high-density (i.e. number per unit area) Ag nanosheets (ANS) with large electrochemically active surface area and rich edge active sites over Ag plates were synthesized via a facile electrodeposition approach in a double electrode system at a constant current of -1 mA for 1800 s. By adjusting the concentration of H3BO3 (0.5 M, 0.1 M and 0.05 M), which is used to control the growth direction of ANS, ANS-20, -50, -350 were obtained with varying thickness of 20 nm, 50 nm, and 350 nm, respectively. Notably, ANS-20 showed a remarkable current density of -6.48 mA cm-2 at -0.9 V versus the reversible hydrogen electrode (RHE), which is almost 1.6 and 2.4 times as high as those of ANS-50 and -350, respectively. Furthermore, ANS-20 exhibits the best CO selectivity of 91.2% at -0.8 V versus RHE, while the other two give 84.6% and 77.9% at the same potential. The excellent performance of ANS-20 is attributed to its rich edge active sites and large electrochemically active surface area (ECSA).

Au aerogel for selective CO2electroreduction to CO: ultrafast preparation with high performance.

Noble metal aerogels (NMAs) have been used in a variety of (photo-)electrocatalytic reactions, but pure Au aerogel (AG) has not been used in CO2electroreduction to date. To explore the potential application in this direction, AG was prepared to be used as the cathode in CO2electroreduction to CO. However, the gelation time of NMAs is usually very long, up to several weeks. Here, an excess NaBH4and turbulence mixing-promoted gelation approach was developed by introducing magnetic stirring as an external force field, which therefore greatly shortened the formation time of Au gels to several seconds. The AG-3 (AG with Au loading of 0.003 g) exhibited a high CO Faradaic efficiency (FE) of 95.6% at an extremely low overpotential of 0.39 V, and over 91% of CO FE was reached in a wide window of -0.4 to -0.7 V versus the reversible hydrogen electrode (RHE). Partial current density in CO was measured to be -19.35 mA cm-2at -0.8 V versus RHE under 1 atm of CO2. The excellent performance should be ascribed to its porous structure, abundant active sites, and large electrochemical active surface area. It provides a new method for preparation of AG with ultrafast gelation time and large production at room temperature, and the resulting pure AG was for the first time used in the field of CO2electroreduction.

Facile synthesis of flower-like hierarchical N-doped Nb2O5/C nanostructures with efficient photocatalytic activity under visible light.

Significant endeavors have been devoted in the past few years to establish efficient visible light-activated photocatalysts. Herein, we successfully synthesized a flower-like hierarchical nitrogen-doped and carbon-sensitized Nb2O5 (NBO) nanostructure (denoted N-NBO/C). The as-prepared N-NBO/C possessed a specific surface area of 260.37 m2 g-1 and single wire diameter of less than 10 nm. The effect of reaction parameters such as hydrothermal reaction time, temperature and concentration of hexamethylenetetramine (Hmta) on the morphology of NBO was systematically investigated to elucidate the growth mechanism. The carbon on the surface and the nitrogen in the framework of NBO are beneficial for light harvesting, visible light absorption, formation of oxygen vacancies, and electron-hole separation. The photocatalytic performance of the as-fabricated N-NBO/C nanostructures was estimated via the photodegradation of 30 mg L-1 RhB, where greater than 98% of RhB was decomposed within 30 min upon visible-light radiation. Hence, the obtained N-NBO/C nanostructure exhibits much higher photocatalytic activity for the decomposition of RhB upon visible light irradiation than that of pure niobium oxide (NBO), nitrogen-doped titanium oxide (N-TIO), and nitrogen-doped niobium oxide (N-NBO). This work supplies a versatile route for the synthesis of nitrogen-doped and carbon-sensitized metal-oxide nanostructures for possible utilization in solar energy transformation and environmental remediation.

Facile route for C-N/Nb2O5 nanonet synthesis based on 2-methylimidazole for visible-light driven photocatalytic degradation of Rhodamine B.

Herein, we fabricated a C and N co-modified Nb2O5 nanonet structure (C-N/Nb2O5NNs) from niobium oxalate using 2-methylimidazole (Hmim) as a source for C and N via a simple hydrothermal route. The obtained nanonets are robust and cost-effective with excellent recycling stability. Compared with N-doped TiO2 (N-TiO2) and a Nb2O5 control sample (Nb2O5-CS), the resulting nanonets exhibited the highest performance toward the photocatalytic degradation of Rhodamine B (RhB) upon visible light irradiation (λ > 420 nm). Through this study, we revealed that the synergetic effects of C and N on the nanonet surface, which were effectively incorporated into the surface of the Nb2O5 nanonet structure, not only remarkably enhanced the visible light response by decreasing the bandgap to 2.9 eV but also improved the light utilization efficiency and photo-induced electron-hole pair separation efficiency of our nanonet structure. We also proposed that the presence of carbonate species (CO x ) and nitrogen species (NO x ) increased the population of generated holes (h+) that had the key role in the photodegradation mechanism of RhB, suggesting reasonable importance for the modification of Nb2O5 with C and N. This synergism offers a new view to reveal the origin of photodegradation processes, introducing h+ as a key intermediate. Our approach provides a new insight to design 2D nanostructures with potential applications in catalysis, solar energy conversion, and environmental protection.