The electrochemical nitrogen reduction reaction (NRR) to produce NH3 is the most efficient, eco-friendly and cost-effective alternative to the Haber-Bosch process. It is crucial to investigate and develop electrocatalysts selective for NH3 synthesis. In recent studies, the Ti3C2 MXene has emerged as a highly promising electrocatalyst for the NRR process. In this work, we explore the effect of Zif-8 addition over MXene sheets in order to control the rate of hydrogen evolution reaction (HER). Despite the better result obtained for Zif-8@Ti3C2 (3.0 μg NH3 gcat-1 h-1 at -0.55 V/RHE), the ammonia produced when using Zif-8@Ti3C2 as cathode material is shown to be originated from nitrogen atoms contained in the Zif-8 structure instead of those of N2. The results shed light to the need to fully understand the N2 electroreduction process over N-containing electrocatalysts.