Nickel polyphthalocyanine with electronic localization at the nickel site for enhanced CO2 reduction reaction

Nickel phthalocyanine (NiPc) can be at first glance a compelling catalyst for CO2 reduction reaction (CO2RR) because of its Ni–N4 site. Unfortunately, the pristine NiPc possesses a low catalytic activity resulting from the poor CO2 adsorption and activation capabilities of the electron-deficiency Ni site. Herein, we develop nickel polyphthalocyanine (NiPPc) with extended conjugation to tailor the electronic density at the Ni active site. The enlarged π conjugation of NiPPc evokes the d-electrons localization, increasing the electronic density at the Ni site, which enhances its CO2 adsorption and activation. Consequently, NiPPc supported on carbon nanotubes (NiPPc/CNT) in a flow cell delivers an excellent activity of −300 mA cm−2 for CO2RR with the CO selectivity of 99.8%, which is much higher than that of NiPc dispersed on carbon nanotubes. NiPPc/CNT exhibits an outstanding stability for CO2RR of more than 30 h at a current density of −100 mA cm−2 with an ultrahigh selectivity for CO, exceeding 99.7%. This work showcases a new way of tuning the electronic density of catalytic sites.