To date, nanoparticles as catalysts for green hydrogen have been like rowers in an eight: researchers could only measure their average performance, but couldn’t determine which one was the best. Scientists have demonstrated that cube-shaped cobalt oxide nanoparticles are more efficient than spherical ones. This paves the way for the systematic design of cost-effective and efficient catalysts for green hydrogen.To date, nanoparticles as catalysts for green hydrogen have been like rowers in an eight: researchers could only measure their average performance, but couldn’t determine which one was the best. Scientists have demonstrated that cube-shaped cobalt oxide nanoparticles are more efficient than spherical ones. This paves the way for the systematic design of cost-effective and efficient catalysts for green hydrogen.