AFAIK, ceramic membranes work perfectly well as exchange elements for hydrocarbon-oxygen fuel cells; but I have no idea why they aren't being used everywhere. It used to be mostly due to longevity issues, but I haven't kept up.
Also, Faradaic efficiency is not the total efficiency. For a fuel cell it would automatically be close to 100% anyway, while total efficiency is normally much lower.
Especially if said contaminants include stuff like H2C2. That can be rather explosive. And might accumulate somewhere in the plumbing, unsuspected until ...
Ethylene, on the other hand, is a chemical feedstock used for many products. There's been a longstanding effort to upgrade methane to ethylene because the latter is so much more valuable.
For on-site "methane battery" uses, it's probably fine if your methane is fairly contaminated with a known-when-you-designed-the-system mess of somewhat-higher hydrocarbons.
But from a quick search, gas and power utilities seem very much concerned with higher hydrocarbons in their methane. And "higher" = "worse". Which makes sense. Those would alter the proper fuel/air ratios, and probably impact emissions. And they do not want liquid hydrocarbons to condense inside their high-pressure gas lines in cold weather, then cause "water hammer" damage to equipment.
> Carbon dioxide offers a unique opportunity as a feedstock for energy production through electrocatalysis. Methane production holds promise for its widespread applications and market demand. However, commercial viability faces challenges of low selectivity, current density, and high applied potential. Efforts to improve methane selectivity while suppressing multi-carbon products, e.g., ethylene, often involve lower alkalinity electrolytes. However, it reduces current density due to increased ohmic resistance without significant gains in the reaction yield. This study utilizes quantum mechanics computations to design a nano-cluster copper catalyst that redirects the reaction pathway from ethylene towards methane, even under alkaline conditions. We achieved a Faradaic efficiency (FE) of 85 %, a current density of 1.5 A/cm2, and stability of over 10 hours solely by controlling particle size in copper catalysts. This work paves the way to overcoming current limitations in electrocatalytic methane production and holds broader implications for advancing sustainable CO2 utilization in energy systems.
Also of interest - could this electrochemical setup be run in reverse, as a methane fuel cell? That I'm aware of, 85% efficiency would be far better than the current state of the art there.