A comprehensive approach providing a new synthetic route for bimetallic electrocatalysts via isoPOMs [M/Rh(Cp*)4W8O32] (M = Rh (1) and Ir (2))

Abstract

Polyoxometalates (POMs) are highly versatile materials if paired with various conducting supports. We here present a new prospective approach for obtaining advanced electrocatalytic systems via POMs (1 and 2) nanostructured on Ni foam (NF) to give bimetallic nanohybrid composite materials M_0.4Ni_0.6/WO₃ (M = Rh (3) or Ir (4)). By this pathway, two rare isopolyoctatungstate-based organometallic clusters [H_x(MCp*)₄W₈O₃₂]·yH₂O (in 1, M = Rh, x = 8, y = 23; in 2, M = Ir, x = 4, y = 17.33) have been synthesized via one-pot reactions using [Cp*MCl₂]₂ (Cp* = pentamethylcyclopentadienyl, M = Rh or Ir) and Na₂WO₄·2H₂O in basic conditions. Compounds 1 and 2 were successfully nanostructured on the surface of commercially available NF and were thermally reduced to M_0.4Ni_0.6/WO₃ (M = Rh (3) or Ir (4)) after annealing at 400 °C for 8 h in a 15% H₂/N₂ atmosphere. Electrodes modified with the POMs 3 and 4 exhibited remarkable HER activities in a 1 M KOH solution and achieved a current density of 10 mA cm⁻² at low overpotentials of about 67 and 35 mV versus RHE, with Tafel slopes of 56 and 34 mV dec⁻¹, respectively.