Honda's FCV sedan will come to market next year. The FCV is an electric car powered by a hydrogen fuel cell. Honda and GM have been working together on fuel cells. Image source: Honda.

General Motors' (GM -2.48%) global product chief, Mark Reuss, let slip something interesting during a presentation to investors earlier this month: GM is working on new technology with a partner that might surprise you -- Honda (HMC -2.29%).

What's that about?

An alternative -- or complement -- to battery-electric cars
We don't (yet) know what else the two might be working on, but we have known for a while that GM and Honda are working together to develop a fuel cell suitable for mass-market vehicles. The technology is expected to come to market around 2020. 

Fuel cells are devices that extract energy from a substance, usually hydrogen gas, and chemically convert it to electricity. The only "exhaust" from a hydrogen fuel cell is water vapor. 

The devices hold promise as a way to power electric vehicles. But one key obstacle has been cost: Current fuel cells incorporate costly materials like platinum. And the devices have been heavy and cumbersome. 

Honda has been tinkering with fuel cells for many years, deploying little fleets of fuel-cell cars in places like Southern California. Honda recently confirmed that it will bring a fuel-cell vehicle to market next year, following rival Toyota's fuel-cell-powered Mirai.

GM has been doing fuel-cell research since the 1960s
It's less well known that GM has been working on fuel cells for much longer. In fact, GM built the very first operational vehicle powered by a fuel cell way back in 1968, and the company has received more patents on technology related to fuel cells since 2002 than any other company. 

GM has expertise in some technologies that are especially applicable to mass-market fuel cells, like the ability to apply very thin but uniform coatings to parts.  Meanwhile, Honda has been able to reduce the size of its fuel-cell apparatus, called a "stack," to about the same size as its 3.5-liter V6 engine. 

That means it can be placed under a car's hood. Current electric cars require a lot of space for batteries or fuel-cell components, and that space often comes out of the passenger compartment.

If Honda is contributing advances in size, and GM is contributing advances that help lower costs, it's easy to see how the two might have decided to team up.

Honda appears to be betting on fuel cells...
Many electric-car proponents have been dismissive of fuel-cell technology. They say that batteries are a greener solution, that there's more infrastructure already in place to support them, and that hydrogen fuel cells are an expensive distraction. Tesla Motors CEO Elon Musk has derided them as "fool cells" (and not "Fool" in the sense that we like around here).

Honda, like Toyota, clearly sees it differently. Toyota has said that its engineers think that the long recharging times required by battery-electric cars will turn out to be an insurmountable obstacle to mass-market adoption of the technology.

... but for GM, fuel cells are just one of several big bets
GM doesn't seem to agree. It doesn't see fuel cells versus batteries as an either/or choice. Reuss said during his presentation that fuel cells may work better for larger vehicles than batteries. It could also turn out to be more cost-effective where longer range is required -- making the car's hydrogen tank larger will likely always be cheaper than adding more batteries. 

The Chevrolet Bolt is an affordable battery-electric car with about 200 miles of range. GM will bring it to market in late 2016 or early 2017. Image source: General Motors.

GM is obviously also putting a lot of effort into battery electrics. It's bringing a mass-market battery-electric car, the Chevrolet Bolt, to market in a little over a year. It's also extending its very good plug-in hybrid technology, developed for the original Chevy Volt, to more products across its range -- including the new top-of-the-line Cadillac CT6 sedan.

But it's clear that GM is taking a mixed approach to the future of autos -- and it's obvious that GM and Honda have found some real value in working together.