The synthesis of ammonia as a precursor to fertilizer is estimated to support the nutritional needs of over 40% of the world's population. Furthermore, ammonia is a promising carbon-free fuel and hydrogen carrier for applications in sustainable transportation and energy storage. Ammonia is most commonly synthesized by the Haber-Bosch process, using hydrogen produced from methane reforming and energy generated from hydrocarbon combustion, and accounts for nearly 2% of global carbon emissions. There are two primary approaches to decarbonize ammonia synthesis: the "Green" Haber-Bosch process using hydrogen produced via water electrolysis or solar thermochemical water splitting, and the electrochemical nitrogen reduction reaction (NRR). NRR provides the advantages of distributed, load-matching production to generate ammonia near its point of use, and can provide lower capital and operating expenses than the "Green" Haber-Bosch process. However, current electrocatalysts for NRR are limited by poor selectivities and/or low activities that make commercialization infeasible. Efforts to improve the performance of NRR electrocatalysts are therefore essential for the development of a sustainable ammonia synthesis process.