Electrochemical CO2 reduction reaction (CO2RR) is a promising alternative
to deal with CO2 and generate
green energy. Carbon monoxide (CO) is one key desired product of the
CO2RR. Herein, a Mn-based heterogeneous catalyst by depositing
MnO nanoparticles on three-dimensional N-doped graphene aerogels (NGAs)
is synthesized. The catalyst exhibits a negligible onset potential
of −0.27 V (vs RHE). This onset potential is 12.5% lower than
that of bulk Au electrodes. Moreover, the higher Faradaic efficiency
for CO is 86% at a potential of −0.82 V (vs RHE) and better
stability over at least 10 h. The excellent CO2RR performance
can be attributed to the large specific area of the unique 3D crumpled
porous NGA nanostructure, the synergistic effect of well-crystallized
MnO active sites, and effective hydrogen evolution reaction suppression
from nitrogen doping. The enhancement effect is also revealed by the
density functional theory method. Our results highlight a promising
new class of low-cost, abundant electrocatalysts for synthetic fuels
from CO2.
The chemical and physical characteristics of PM 2.5 , especially their temporal and geographical variations, have been explored in metropolitan Hangzhou area (China) by a field campaign from September 2010 to July 2011. Annual average concentrations of PM 2.5 and PM 10 during non-raining days were 106-131 µg•m −3 and 127-158 µg•m −3 , respectively, at three stations in urban breathing zones, while corresponding concentrations of PM 2.5 and PM 10 at an urban background station (16 m above ground level in a park) were 78 and 104 µg•m −3 , respectively. For comparison, the annual average PM 10 concentration at a suburban station (5 m AGL) was 93 µg•m −3. Detailed chemical analyses were also conducted for all samples collected during the campaign. We found that toxic metals (Cd, As, Pb, Zn, Mo, Cu, Hg) were highly enriched in the breathing zones due to anthropogenic activities, while soluble ions (, 2 4 SO 3 NO , 4 NH ) and total carbon accounted for majority of PM 2.5 mass. Unlike most areas in China where sulfate was several times of nitrate in fine PM, nitrate was as important as sulfate and highly correlated with ammonium during the campaign. Thus, a historical shift from sulfate-dominant fine PM to nitrate-dominant fine PM was documented.
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