Pd doping-weakened intermediate adsorption to promote electrocatalytic nitrate reduction on TiO2 nanoarrays for ammonia production and energy supply with zinc-nitrate batteries

The (photo)electrochemical nitrogen reduction reaction for ammonia (NH3) production is an appealing alternative to the traditional high-energy Haber-Bosch reaction. However, the future of this approach is bleak because of the ultralow N-2 solubility and the nonpolar N N bond causing the NH3 yield and selectivity to be unsatisfactory. Nitrate electroreduction (NORR) into NH3 brings promise for the future landscape of NH3 electrosynthesis due to the low N = O bond energy and high nitrate solubility. Here, we report a highly efficient Pd-doped TiO2 nanoarray electrode for NH3 production from the NORR. With weakened adsorption abilities to the intermediates induced by Pd introduction, the catalyst delivers a record-high NH3 yield of 1.12 mg cm(-2) h(-1) (or 0.066 mmol cm(-2) h(-1)), an impressive NH3 faradaic efficiency (FE) of 92.1%, and an exceptional nitrate conversion of 99.6%. Considering an eight-electron nitrate-to-ammonia reaction and the excellent electrocatalytic activity of Pd/TiO2, we, for the first time, propose and develop a Zn-nitrate battery system, which delivers striking bifunctionality for harnessing the electrons related to the NORR to generate electricity and directly produce NH3, specified by a power density of 0.87 mW cm(-2) and a high NH3 FE of 81.3%. Our work not only verifies the positive effect of Pd doping on facilitating the NORR, but also demonstrates a galvanic nitrate-based cell providing a promising strategy for NH3 production and broadening the field of Zn-based batteries.