CO2 is a big issue, and only getting bigger. Whether or not you believe it's causing global warming, the reality is it's being watched closely and will be controlled in the future, in many places it already is.
While our reliance on fossil fuels is deep, alternatives are gaining ground such as electrics, where batteries still remain problematic and imperfect.
Carbon capture is another imperfect solution - we can collect the CO2 from individual sources like a smokestack, but what do we do with it? Sequestering the carbon dioxie in high pressure underseas or underground is an impermanent solution with big risks, and utilizing CO2 has limited usefulness - like carbonating your soft drinks, and those options don't prevent it from winding up in the atmosphere in the end anyway.
Hydrogen is another option which could work well as a fuel - anywhere from small scale distributed systems like cars, trains and trucks - some are already in production and use, all the way to bigger scales like offsetting natural gas in combined cycle turbines - up to 30% may be possibly to replace directly and directly offsets the CO2 from natural gas combustion.
Hydrogen also has potential in carbon capture and utilization - instead of trying to bury CO2, it's possible to make use of it, reacting H2 and CO2 to form synthesis gas that can be used to make methanol, which if nothing else is a more permanent storage than compressed CO2.
Hydrogen also has enormous use in industrial purposes - and that's where the majority is used, specifically for ammonia production and petroleum refining, but also it's a raw material for many other chemicals.
So, hydrogen! we use a lot, and likely may use more in efforts to combat CO2. The problem is, producing H2 makes CO2! Almost all hydrogen produced today comes from steam methane reforming, CH4 + 2 H2O --> 4 H2 + CO2. Most of the rest comes from electrolysis, which is not very efficient and really is just an energy storage - the energy you get from combusting H2 to H2O is the energy you have to put back in to split it back to hydrogen again (plus any inefficiencies of the system). and most of that energy is coming from power plants already burning fossil fuels
So how can we make H2 without CO2?
A few ways, some neat academic scale ideas like direct solar photoelectrolysis can make hydrogen, but not at large scale. Electrolysis can work, but to be CO2 free the energy needs to come from renewable sources - and it's a lot of energy. On the other hand the nice thing about fossil fuels is nature's already made the energy carrier, we get energy from combustion instead of supplying the energy to reverse it. and right now and forseeable future, natural gas is cheap and abundant.
Instead what if we can take the hydrogen from natural gas, but leave the carbon as SOLID CARBON?! That's methane pyrolysis - CH4 --> C + 2 H2. It takes abundant CH4 to produce hydrogen, same starting point as most hydrogen already produced via SMR, but instead of CO2 you've got solid carbon, which at best can find use and be sold as a valuable material, at worst it's easy to dispose of - we could even back fill in the old coal mines, a cute idea some researchers in the field have proposed. Unfortunately this takes more energy and produces less H2 per CH4 than SMR does currently. But it's close, a lot closr than electrolysis, and a CO2 tax or sale value of the carbon byproduct can push it ahead of SMR in terms of economics.
It seems like an easy idea, but to actually do it is much less simple. Put energy into CH4 and get out C and H2! Well, One big issue is the carbon. C looks great in an equation on a piece of paper, but you know what doesn't a big pile of soot. And that's what you get - consider the fact that carbon with a molecular weight of 12 versus hydrogen with a MW of 1, in CH4 75% of the mass is carbon. that means for every ton of hydrogen you're making 3 tons of carbon. with global hydrogen demands (*2013) at >60 Million tons, that's a lot of carbon. And whatta ya do with that much carbon, picture the bad kid getting a lump of coal from santa. well now you've got enough to give every kid on the planet almost 100 kilos of coal, every Christmas. In a lot of the academic research you see people suggesting the hydroge is made, and you "sell the carbon" and proceed to give a value for selling "carbon" in the range of $20 a ton for coal to >1k/kilogram for nanofibers. But that totally neglects that all of those markets have very specific demands. Lets take a look at carbon markets - you've got high value with specialty nanofiber materials, but the demand is tiny. meanwhile big volume sinks exist in coking for steel, but those values are small. Not to mention each of these requires specific properties and purities of carbon, which have decades of careful research into their production.
The other big issue is how do you put the energy in. Splitting CH4 takes temperatures of 1200°C and above. that could come from a plasma arc, electric heating elements, even burners, but the trickier part is the heating also affects what type of carbon you get out.
Alright, that's a good place to take a step back and look at the history.