Ti3C2Tx-Supported Polyoxometalate@Cu-BTC Composites for Electrocatalytic Nitrate-to-Ammonia Reduction

Abstract

The electrocatalytic nitrate reduction reaction (eNO₃RR) offers an effective pathway for carbon-neutral ammonia synthesis; however, its efficiency is severely hampered by the intricate thermodynamics of proton-coupled electron transfer (PCET) and by competition from the hydrogen evolution reaction (HER). To address these challenges, we engineered two ternary composite catalysts (PMo₁₂@Cu-BTC/Ti₃C₂T_x and PW₁₂@Cu-BTC/Ti₃C₂T_x) incorporating distinct polyoxometalate anions (H₃PMo₁₂O₄₀, noted as PMo₁₂; H₃PW₁₂O₄₀, noted as PW₁₂) by integrating polyoxometalate-based metal−organic frameworks (POMOFs) with a Ti₃C₂T_x MXene scaffold. This architectural design synergistically couples redox-active POMOFs, facilitating optimized PCET, with a three-dimensionally interconnected porous MXene network, effectively mitigating the inherent inferior conductivity of POMOFs. Comparative studies reveal that the phosphomolybdate (PMo₁₂)-based catalyst exhibits superior electrocatalytic activity, achieving an NH₃ yield of 12.86 mg h⁻¹ mg_cat.⁻¹ at −0.8 V vs RHE, alongside a large electrochemical active surface area (ECSA) and exceptional stability. This work validates the significant potential of the POMOF−MXene hybrid platform in reducing the competing HER and promoting eNO₃RR, offering a viable strategy for decentralized wastewater treatment and green ammonia synthesis.