The vast majority of power/energy generation in our global economy is based on the chemical element carbon, specifically fossil carbon (coal) and hydrocarbon (oil and gas) fuels. Such an economy is not sustainable in the medium- to long-term for two fundamental reasons; first, there exists only a finite amount of fossil fuel, and, second, the carbon dioxide released during the combustion of fossil fuels induces anthropogenic climate change with costly and potentially disastrous consequences. Current energy technologies cannot support both a reduction in carbon dioxide emissions and an ever-expanding global economy. It is now recognized that hydrogen may be one of the leading contenders as a potential solution for a sustainable alternative to fossil fuels, especially for transport and for heat and power generation and energy storage. However, any transition from a carbon-based (fossil fuel) energy system to a hydrogen-based economy involves significant scientific, technological and socio-economic barriers. Our aim is to illustrate the "hydrogen nexus" as a possible connection or link from today's carbon economy to a sustainable energy future centred on hydrogen.