Integration of a non-precious pyrolyzed Cu-doped ZIF as an oxygen depolarized cathode in an advanced chlor-alkali electrolyzer

Abstract

Oxygen reduction is the critical step in advanced chlor-alkali electrolysis, which has motivated extensive research in catalyst development for improved efficiency and durability. This study investigates the oxygen reduction reaction (ORR) on Cu-based electrocatalysts supported on N-doped carbon (Cu/NC), derived from a Cu-modified zeolitic imidazolate framework (ZIF), and their ultimate performance in a chlor-alkali electrolyzer. Through comprehensive electrochemical characterization in 0.1 M NaOH solution, values of E_onset = 0.87 V and E_1/2 = 0.75 V (vs. RHE) were obtained, which are competitive with commercial Pt/C despite the superior j achieved by the latter in LSV tests. The electron transfer number (n) of the optimum Cu/NC was 4, very close to benchmark catalyst Pt/C 20 wt. % (n = 3.94). Cu/NC had a low Tafel slope (128 mV dec⁻¹), thus speeding up the ORR on this nanocatalyst. Additionally, chronoamperometry and accelerated durability tests demonstrated the long-term stability of Cu/NC for 10 h. The catalyst was assembled as an oxygen depolarized cathode (ODC) in a purpose-designed advanced chlor-alkali electrolyzer, resulting in a cell voltage of 2.1 V at 1 kA m^-2 and 80 °C, which underscores the potential of Cu-based nanocatalysts in electrochemical energy devices. This research serves to leverage insights for the use of advanced electrocatalysts to enhance the efficiency and sustainability of chlor-alkali electrolysis.