Electrocatalytic activity and volatile product selectivity for nitrate reduction at tin-modified Pt(100), Pd(100) and Pd–Pt(100) single crystal electrodes in acidic media

Highlights: • Sn/Pt(100), Sn/Pd(100) and Sn/Pd–Pt(100) were prepared for the nitrate reduction. • Gasous products for the electrochemical NO₃RR were analyzed using OLEMS. • Sn/Pd(100) and Sn/Pd-Pt(100) produced N₂ but not Sn/Pt(100). -- Abstract: We prepared Sn-modified Pt(100), Pd(100) and Pd–Pt(100) single crystal electrodes and investigated the nitrate reduction reaction (NO₃RR) activity and the product selectivity for them using online electrochemical mass spectroscopy (OLEMS), also known as differential electrochemical mass spectroscopy (DEMS). OLEMS measurements allowed us to quantify volatile products of N₂, N₂O and NO and confirm the production of N₂ at Sn/Pd(100) but not at Sn/Pt(100). Pd-doping to Pt(100) with a 3 atomic % increased the product selectivity for the NO₃RR to N₂. These results indicate that the presence of Pd in the (100) surface is the key to produce N₂, which seems to be related to the hydrogen adsorption energy to the metal surface. The suppression of hydrogenation of intermediate species at the electrode surface could lead to the production of N₂. This work will guide us to understand N₂ production mechanism for the NO₃RR and develop highly selective electrocatalysts for denitrification.