Anion-regulated cobalt coordination polymer: Construction, electrocatalytic hydrogen evolution and L-cysteine electrochemical sensing

Considering that the construction of molecular catalysts with regulatory and determinate structural are conducive to the rapid development of electrical/chemical energy conversion system. Three anion-regulated Co(II) coordination polymers (CPs 1–3) with the chemical compositions of {[CoL(tp)(H2O)2]•2H2O}n (1), {[Co8L4(btc)4(H2O)16](formate)(btc)•DMF•0.5MeOH•0.5Me2NH•36.5H2O}n (2), and {[Co2L(fum)2(H2O)2]•2DMF•3H2O}n (3) (L = bis(1-(pyridin-4-ylmethyl)-benzimidazol-2-ylmethyl)ether, tp = terephthalate, btc = 1,3,5-benzenetricarboxylate, fum = fumarate), have been synthesized using the solvothermal method by introducing different anion. Single crystal analysis shows that the CPs 1 and 3 possess 2D layer structure, while CP 2 shows 1D hollow column structure. The electrocatalytic hydrogen evolution and the L-cysteine electrochemical sensing properties of carbon paste electrode modified with Co(II) CPs (CPEs 1–3) were investigated respectively. The hydrogen evolution reaction (HER) properties of CPEs 1–3 were studied in 0.5 M H2SO4, the results show that 1–3 exhibit overpotentials of –695, –780 and –801 mV at the current density of 10 mA cm–2 with Tafel slopes of 210 ∼ 273 mA dec–1, which confirming that they all have effective electrocatalytic HER ability. The catalytic mechanism of CPs 1–3 was inferred from the determined structure, which showing that the reason for the catalytic performance order of 1 > 2 ≥ 3 may be due to the difference in the number of coordinated water molecules. Electrochemical sensing studies show that CPs 1–3 have low detection limits of 0.43, 0.78, and 0.65 μM for l-cysteine ​​in the response ranges of 0.5 μM ∼ 4.0 mM, 1 μM ∼ 4.0 mM, and 1 μM ∼ 4.0 mM, and sensitivity of 8.09, 7.20 and 10.84 μA mM–1. Therefore, the three Co(II) coordination polymers are effective dual-functional electrocatalysts.