Scientists have long dreamed of mimicking photosynthesis, by using the energy in sunlight to knit together hydrocarbon fuels from carbon dioxide and water. Now, a cheap new chemical catalyst has carried out part of that process with record efficiency, using electricity from a solar cell to split carbon dioxide (CO2) into energy-rich carbon monoxide (CO) and oxygen. The conversion isn’t yet efficient enough to compete with fossil fuels like gasoline. But it could one day