Design and Synthesis of Lead(II)-Based Electrocatalysts for Oxygen Evolution Reaction

A well-organized worldwide effort in providing remedies to sustainable clean energy generation and storage has focused on the strategic design and development of stable and efficient earth-abundant metal (Fe, Co, Ni, Pb, etc.)-based electrocatalysts for the oxygen evolution reaction (OER). Unfortunately, examples of Pb-based catalysts for such a process are rare. In this work, based on the dual-linker strategy, we have designed and synthesized two new two-dimensional (2D) coordination polymers of Pb with the hcb topology, [Pb₂(tpbn)(adc)₂]·4H₂O·0.5CH₃OH} (CP1) and {[Pb₂(tpbn)(fum)₂]·7H₂O} (CP2), in excellent yields by the room-temperature self-assembly of Pb(OAc)₂, tpbn, and H₂adc or H₂fum (where tpbn = N,N',N‴,N‴'-tetrakis-(2-pyridylmethyl)-1,4-diaminobutane, H₂adc = acetylene dicarboxylic acid, and H₂fum = fumaric acid). In addition to determining their X-ray single crystal structures, the phase purity and thermal stability were established by powder X-ray diffraction and thermogravimetric analysis, respectively. Furthermore, these were also characterized by the microscopic techniques (SEM/EDX and TEM/HRTEM). For their conductive and highly stable nature in alkaline medium, both CP1 and CP2 were tested for their suitability in the OER process. Interestingly, with a subtle change from adc in CP1 to fumarate in CP2 as the dicarboxylate linker, the latter performed much better than the former and displayed an excellent electrochemical stability in basic medium. Remarkably, CP2 has one of the lowest Tafel values (35 mV dec^-1) and a low overpotential value (140 mV vs RHE) in 0.5 M KOH compared to those reported for any materials. Such a comparative study with CP1 and CP2, which are the simplest CPs and made with green-chemistry protocols for an easy making in large quantities, provides an outlook to developing the next-generation Pb-based electrocatalysts.