In fact, the reduction potential increases by about 59 mV for each pH unit of acidity. The more acidic the solution, the easier it is to transfer electrons on to CO2 to produce formate or formaldehyde. Unfortunately, exactly the same applies to hydrogen. The more acidic the solution, the easier it is to transfer electrons on to protons to form H2 gas. Simply changing pH therefore has no effect at all. It remains impossible to reduce CO2 with H2.
