The rapid increase in atmospheric carbon dioxide levels has become a pressing concern for global climate change. Electrocatalysis has emerged as a critical pathway for decarbonizing chemicals and fuels, particularly in the production of hydrogen and ammonia, given the intensive carbon emissions associated with conventional chemical engineering plants. In this thesis, we systematically address the current challenges within electrocatalytic water splitting and nitrate reduction reactions, which are critical processes for green hydrogen and ammonia synthesis. We first investigated mechanistic insights into the stability challenges of oxygen evolution reaction catalysts, alongside practical considerations for reactor design. A non-iridium-based electrocatalyst was then developed to reduce costs and enhance durability for the acidic oxygen evolution reaction, integrated into a proton exchange membrane electrolyzer to facilitate efficient green hydrogen production. Additionally, we investigated an oxide alloy catalyst system aimed at further reducing noble metal loading while enhancing catalyst activity. Furthermore, we examined electrochemical nitrate reduction as an alternative pathway for green ammonia production, focusing on the design and synthesis of catalysts for efficient conversion. Moreover, we designed a solid electrolyte reactor and coupled it with a cation shuttling process to advance the direct conversion of waste nitrate streams into green ammonia. The catalyst design and electrolyzer engineering strategies proposed in this dissertation contribute meaningfully to the development of electrochemical technologies crucial for sustainable energy and resource management.