Enhanced Per-Site Electrocatalytic H 2 Evolving Activity of Cobalt in Co/Ni-Dithiolene-Based Heterometallic Metal–Organic Frameworks

Heterometallic metal–organic frameworks (MOFs) consisting of electrocatalytically active metal ions paired with relatively inactive metal ions have shown enhanced per-site activity in the form of large turnover numbers observed for the active metal, however, at the expense of lower faradaic efficiencies (FEs). This technique has been employed to construct electrocatalysts for small molecule activation transformations, such as CO 2 reduction or the hydrogen evolution reactions (HER). In this study, HER-active Co metal-ions were doped into the moderately HER active Ni-triphenylenehexatiolate ( NiTHT ) coordination polymer backbone. The resulting series of polycrystalline Co/Ni-THT MOFs containing as low as 5% Co showed a catalytic overpotential of −256 mV vs RHE with a Tafel slope of 65 mV dec –1 . A 211-fold increase in the turnover frequency per Co, compared to the Co-only analog was observed. This dramatic improvement in per-site activity is complemented by a robust overall performance, where the catalyst showed 98% FE toward H 2 production and demonstrated stable operation for over 17 h of continuous electrolysis.