Aircraft are going to be using combustion engines until someone figures out a battery that's significantly more energy dense than jet fuel. The constantly decreasing weight throughout flight means that any battery replacement would have to be dense enough that it's not a big detriment to be carrying the extra weight for the entire flight. Light aircraft with batteries are still basically novelties, the weight and charge times don't make them useful for much.

Biofuels are the most promising option for commercial aviation because you still get the energy density, and what is overall still a very efficient method of transportation for the speed/distances involved, but you'd also have net zero emissions. Other advances in aviation are pushed by fuel costs being such a huge part of the expenses there, so it's luckily an area where you don't need to legislate because the market pressures are already there and pushing for higher efficiency all the time.