Knox, who announced his resignation from Santos in August 2015 after eight years leading the oiler just as profits were tanking amid the worst oil price slump in years, has joined Redflow as a non-executive director.
Knox, who is also on the board of CSIRO, said he was attracted by Redflow's battery technology.
The Brisbane-based company is undertaking an in-depth review of its strategy and direction and increasing production of its unique zinc-bromine flow batteries to meet demand for its ZCell and ZBM2 batteries.
The former Australian Petroleum Production and Exploration Association chairman said Redflow's technology had the potential to affect change in the way energy was used, both for individuals and families at home, small businesses and telecommunications firms.
"The beauty of this battery is it has a real role to play in stabilising our energy supply system as batteries become more widely used," he said.
"We need to get much better at storing energy if we want to reduce our carbon footprint while continuing to provide affordable, reliable energy supplies."
Redflow executive chairman Simon Hackett said Knox brought valuable international business skills to the board in what is set to be a "pivotal and positive year in the life of the company".
"David's presence as a non-executive director will broaden the board's skills base and constructively challenge the executive team at Redflow as they advance both strategy and execution during 2017 and beyond. He understands and supports the unique merits of our energy storage technology," Hackett said.
Knox said Redflow's zinc-bromine flow technology made its batteries safer.
"One of the unique advantages of the Redflow battery is its safety, by which I mean it does not have a fire risk associated with it as lithium does," he said.
"Another benefit of the Redflow battery is that it's happy to be fully discharged for extended periods without damage, unlike other battery types which are degraded or damaged when fully discharged. These are very important factors if you want a reliable long-term battery."