Nitrogen doping and titanium vacancies synergistically promote CO2 fixation in seawater

Abstract

The electrocatalytic generation of useful chemicals from CO₂, H₂O, and sustainable energy resources offers a promising strategy for the carbon cycle. However, the current CO₂ electrolysis system is mainly operated in artificial electrolytes (e.g. ionic liquids and inorganic salt solutions), of which the high cost and impractical working conditions hinder its large-scale development. In this case, seawater represents an attractive alternative due to its abundance and good conductivity. Herein, we show that N-doping and titanium vacancies (V_Ti) can be introduced in Ti₃C₂ MXene nanosheets via a facile NH₃-etching pyrolysis approach. These nanosheets demonstrate impressive CO₂ reduction reaction (CO₂RR) performances in seawater with a remarkable 92% faradaic efficiency and a partial current density of −16.2 mA cm⁻² for CO production, being close to those of noble metal electrodes. Mechanistic studies reveal that the existence of N dopants and V_Ti synergistically modulates the electronic structure of the active Ti site, on which the free energy barriers for the key *COOH formation and desorption of *CO are greatly reduced, thereby leading to a notable CO₂RR improvement. This study provides an opportunity for developing an active and cost-effective CO₂ electrolysis system by using seawater as the electrolyte.