I have a solution of copper(II) sulfate, and I would love to precipitate the copper metal. From looking at the standard reduction potential table, it appears that I can do this by bubbling hydrogen gas through the solution. However, the potential is not very large, so I am unsure of how well this approach would work. I was also wondering if sodium metabisulfite could be used for this purpose. I know I can precipitate copper carbonate with sodium carbonate and reduce with carbon, but this will take more time, and probably result in a large loss of product. I would also like to avoid precipitating the metal with another metal, because I am demonstrating how metals can be isolated so it would be silly to use a metal that is even harder to reduce.
Copper reduced from solution is readily oxidized by air.
When I cared, I made a moderately fine copper powder from citrate. Threat copper salt solution with slight molar excess of sodium (potassium) citrate solution (can be made on site from corresponding hydroxide and easily available citric acid), shake and let the solution stay for a while. It immediately turns deep blue, but the precipitate may appear several minutes later. Filter off the precipitate and then heat on a sand bath at ~200-300 Celsium in a vial plugged with cotton wool. I didn't check if evolved gases are toxic, so use a fume hood or good ventilation. The citrate goes through several changes in color, but eventually produces metallic copper powder. Cool it with wool in. The powder seems to be mildly (inconsistently) pirophoric, so store in a small air-tight container.
Hydrogen on it's own certainly can reduce copper, but the process is neither fast, nor pragmatic.