Matt Horton wants to solve a problem that makes alternative-fuel vehicles unappealing to would-be buyers: lack of convenient places to refuel. Last month, the chief executive officer of Propel Fuels opened the country’s first station where drivers can pump gasoline, ethanol, and biodiesel, cyclists can get tune-ups, and commuters can find public transit schedules. Backed by more than $19 million in venture capital and nearly $12 million in grants from the U.S. Department of Energy and the California Energy Commission, the 23-person Redwood City (Calif.) startup received yesterday an additional, $10.1 million grant from the commission to help build 100 stations around the state in the next four years.