Understanding the physical and chemical basis of device operation is important for their development. While hydrogen fuel cells are a widely studied topic, direct ammonia fuel cells (DAFCs) are a smaller field with fewer studies. Although the theoretical voltage of a DAFC is approximately equal to that of a hydrogen fuel cell, the slow kinetics of the ammonia oxidation reaction hamper cell performance. Therefore, development of anode catalysts is especially needed for practical viability of the DAFCs. To study DAFC operation, specifically interactions between reaction kinetics and different transport phenomena, we developed a one-dimensional model of a DAFC and performed a sensitivity analysis for several parameters related to the cell operating conditions (e.g., temperature, relative humidity) and properties (e.g., catalyst loading). As expected, temperature and relative humidity were very important for cell power. However, while faster reaction kinetics improved the cell performance, simply increasing the catalyst loading did not always produce a comparable enhancement. These and other observations about the relative importance of the operating parameters should help to prioritize and guide future development of and research on DAFCs. Further studies are needed to understand and optimize e.g. humidity management in different scenarios.