Exxon Mobil and FuelCell Energy say that they will jointly work on technology to reduce the cost of capturing carbon emissions from power plants. The companies will try to develop technology that uses carbonate fuel cells to generate power while capturing carbon dioxide, which scientists say is the most prevalent greenhouse gas responsible for climate change, according to AP. It is a sensitive subject for Exxon Mobil Corp., based in Irving, Texas. Officials in several states are investigating the company, which they accuse of misleading investors and the public by understating the risk of climate change. If the fuel-cell approach proves feasible, it could be used in coal- or natural gas-fired plants, the companies said. Shares of FuelCell Energy Inc. jumped 20 percent initially but gave up most of the increase by afternoon trading. Capturing significant amounts of carbon from power plants has been an elusive goal for the fossil-fuel industry. There have been several demonstration projects in the U.S. and elsewhere but they haven't produced the desired results, partly because of high costs. Environmentalists say the money should instead be spent on renewable energy that is cleaner from the start.