The need for clean energy, predominantly wind and sun, to replace fossil fuels is in high demand for the carbon neutrality. The intermittent nature of the renewable energy sources is one of the most important challenges. A potential solution is to store the extra electricity in the form of chemical fuels, and then reconvert on demand. Electrochemical water splitting to produce hydrogen and oxygen is an appealing and sustainable approach. The benchmark electrocatalysts for water electrolysis are noble metal Pt- and Ir/Ru-based materials. Nevertheless, the scarcity and the high cost of these precious catalysts severely hinder their widespread applications. Developing non-precious electrocatalysts has been one long-term target, but still remains a great challenge. In this presentation we will show our research efforts and design strategies by regulating the electronic structures on transition metal-based electrocatalysts for hydrogen evolution, oxygen evolution as well as constructing the water electrolyzer powered by solar energy.