New York Times: A Silicon Valley company is claiming a breakthrough in a decades-old quest to develop fuel cells that can supply affordable and relatively clean electricity. Google, Bank of America, Wal-Mart and other large corporations have been testing the devices, which will be formally introduced on Wednesday. The start-up, Bloom Energy, has raised about $400 million from investors and spent nearly a decade developing a new variety of solid oxide fuel cell, considered the most efficient but most …