Hydrogen (H2) has a high mass-based energy density and produces only water (H2O) as a combustion byproduct in a fuel cell engine. On this basis, H2 is considered one of the most important fuels in any future "net zero carbon" society. At present, natural gas reforming/gasification is widely used to produce H2 because it is the most efficient and least expensive approach. However, this process is neither cost effective nor environmentally friendly. 2, As an alternative, pure H2 (also referred to as green H2) can be obtained from H2O via electrocatalytic techniques. However, the most efficient and durable electrocatalysts currently available for promoting the hydrogen evolution reaction (HER) are nanoparticles (NPs) made from expensive rare metals, such as platinum (Pt), which prevents the widespread adoption of H2 as an affordable fuel. To shift to a "net zero carbon" society, it is indispensable to produce more appropriate catalysts with a higher activity than Pt NP-based catalysts.