Scientists have claimed a milestone in the drive for new energy—development of the first practical artificial leaf, an advanced solar cell that imitates the process，called photosynthesis(光合作用)，that green plants use to make sunlight and water into energy.
“A practical artificial leaf has been a dream of scientists for decades，”said Daniel Nocera，who led the research team．“We believe we have made it．The artificial leaf shows particular promise as an inexpensive source of electricity for homes of the poor in developing countries. One can imagine villages in India and Africa soon purchasing an affordable basic power system based on this technology．”
The leaf is like the shape of a poker card but thinner．Placed in water in a bright sunlight, it could produce enough electricity to supply a house in a developing country with electricity for a day by splitting water into hydrogen and oxygen, which are stored in a fuel cell to produce electricity．
The“artificial leaf”is not a new concept．The first artificial leaf was developed more than a decade ago by John Ttlrner．However, it was impractical for wider use，as it was composed of rare，expensive metals and was highly unstable with a lifespan of barely one day．
Nocera’s new leaf overcomes these problems．It is made of inexpensive materials that are widely available，works under simple conditions and is highly stable．Laboratory studies showed that it could operate continuously for at least 45 hours without a drop in activity．
The key to this breakthrough is Nocera’ s recent discovery of several new powerful, inexpensive catalysts，which are able to accelerate the chemical reaction under simple conditions．Right now, Nocera’s leaf is about 10 times more efficient at carrying out photosynthesis than a natural leaf．Yet he is optimistic that he can boost the efficiency of the device much higher in the future．
21．Daniel Nocera describes his artificial leaf as promising in_________________．
A．making an artificial plant that can feed itself．
B．finding a new kind of catalyst to produce electricity．
C．changing the sunlight and water into electricity directly
D．providing electricity for the poor family at a low cost
22．According to the passage, catalysts in the artificial leaf________．
A．speed up the process of chemical reactions
B．reduce the loss of energy during its operation
C．work as a media to store collected energy
D．slow down the course of chemical reactions
23．The underlined word“it”in the fourth paragraph refers to______．
A．photosynthesis B．catalyst used by the solar cell
C．Turner’s artificial leaf D．Nocera’ s new leaf
24．The passage is most probably from_________．
A．a science fiction story B．a fairy tale book
C．an advertisement for solar products D．a science news report