Interface engineering for improving photoelectrocatalytic performance of 2D/2D MXene@MoS2 for N2 reduction reaction: A theoretical insight

The photoelectrocatalytic nitrogen reduction reaction (NRR) often demonstrates significant catalytic performance due to the synergistic effect of photocatalysis and electrochemistry in synthesizing ammonia (NH3), providing a potential alternative to the traditional Haber-Bosch process. In this paper, we systematically investigated the NRR performance and mechanism of 25 different-ordered hydrophilic MXene composited hydrophobic 2H-MoS2 monolayers constituting the 2D/2D heterojunctions as promising NRR photoelectrocatalysts by first-principles calculations based on density functional theory. The results identified that Cr3C2@MoS2, with lower limiting potentials (-0.20 V, -0.29 V, -0.28 V, -0.23 V, -0.25 V, and -0.25 V, respectively), especially the Mo3C2@MoS2 holds the remarkable catalytic activity with an ultra-low limiting potential of -0.13 V. This phenomenon may primarily be attributed to the efficient interface engineering and the photoelectric synergy effects. The hydrophilic MXene can directly donate H protons to the NRR, thereby shortening the transport pathway for H protons and accelerating the reaction kinetics. Under the action of the interfacial built-in electric field, photogenerated electrons are transferred from MoS2 to MXene, offering an efficient electron transport route, and heightening electron transportability. Furthermore, we introduce the triangle G*NH2 and triangle G*NNH as efficient descriptors to predict the NRR performance. Moreover, the DOS and charge density difference analysis reveal the electron "donation/back-donation" mechanism between N2 molecules and transition atoms, which illustrates the activation effect of N2 molecules. Furthermore, the work function plays a key role in tuning the energy barrier of the potential-determine step, thus affecting the catalytic properties of NRR. Finally, we verified the thermodynamic stability of heterojunctions using AIMD simulation. The modest initial potential, strong visible light absorbance, and exceptional stability endow the MXene@MoS2 heterostructures with substantial promise as a photoelectrocatalyst for nitrogen fixation, thereby charting a viable course toward enhancing the sustainable synthesis of ammonia.