The artificial leaf as a technology panacea has yielded many false starts. The Sun Catalytix project, as reported in an article published May 31, 2012 in “Nature,” has proven more costly than originally anticipated. Apparently the photovoltaic infrastructure costs make the hydrogen yield unprofitable. See the article at: http://www.nature.com/news/artificial-leaf-faces-economic-hurdle-1.10703?WT.ec_id=NEWS-20120529.

The point you raise about using an artificial leaf technology to sequester carbon with formic acid being the principal byproduct and its potential problems, is interesting. Traditionally we manufacture formic acid from CO. Formic acid has many industrial applications – making leather and textiles, as a coagulant in manufacturing rubber, a preservative in livestock and poultry feeds, and an ingredient in the manufacturing of products like toilet bowl cleaners or scale removers. In fact, BASF, announced in May 2012 that they were building a new formic acid production line in Geismar, Louisiana to produce 50,000 tons of the stuff annually. Currently BASF produces 255,000 tons of formic acid to meet industry demand. See the BASF announcement at http://www.basf.com/group/pressrelease/P-12-250.

The CO2 sequestration policy/technology implications are obvious. Any CO2 molecule is equally a CO2 molecule as any other. If you want to sequester a particular power plant’s CO2 emissions, you can do it at any place on Earth. Seems highly unlikely any synthetic photosynthetic scheme could ever compete with photosynthesis in natural tropical rain forests.

In a natural cycle of plant growth the main factor is not sunlight, but water. The world’s great deserts receive twice as much solar energy as tropical rainforests, but little vegetation grows in deserts. There is a reason highly prolific tropical jungles are called “rain” forests.

True, the CO2 naturally sequestered in tropical cellulose is only temporarily sequestered, but what mechanism would permanently sequester billions of tons of formic acid? In the natural environment formic acid would promptly breakdown and oxidize back to CO2. That’s why the whole world doesn’t stink of formic acid.

One could easily imagine a carbon offset scheme where the power-plant utility company in the US would set up CO2 sequestration farms rapidly growing vegetation in distant and sparsely populated tropical regions. We could more reliably and cheaply compress and bury tropical weeds in artificial peat bogs or in the deep oceans than we could store formic acid near power plants.

99% of all the biosphere’s CO2 is already sequestered in the cold ocean depths. Compressed 10-ton bales of tropical cellulose (specific gravity of 1.1) would sink into the ocean depths and remain there forever. Any more permanent sequestration scheme would require conversion into chemically stable carbonates, such as oyster shells and limestone.

I’m not saying inorganic leaves are without value, just that any value couldn’t be in sequestering power plant CO2. Plants are hugely “wasteful” of water; maybe inorganic leaves could play a major role in solar powered hermetically sealed space habitats, but it’s hard to see what a space habitat would do with thousands of tons of formic acid.