Stabilization of High-Valent Molecular Cobalt Sites through Oxidized Phosphorus in Reduced Graphene Oxide for Enhanced Oxygen Evolution Catalysis.

Heterogeneous molecular cobalt (Co) sites represent one type of classical catalytic sites for electrochemical oxygen evolution reaction (OER) in alkaline solutions. There are dynamic equilibriums between Co2+, Co3+ and Co4+ states coupling with OH-/H+ interaction before and during the OER event. Since the emergence of Co2+ sites is detrimental to the OER cycle, the stabilization of high-valent Co sites to shift away from the equilibrium becomes critical and is proposed as a new strategy to enhance OER. Herein, phosphorus (P) atoms were doped into reduced graphene oxide to link molecular Co2+ acetylacetonate toward synthesizing a novel heterogeneous molecular catalyst. By increasing the oxidation states of P heteroatoms, the linked Co sites were spontaneously oxidized from 2+ to 3+ states in a KOH solution through OH- ions coupling at an open circuit condition. With excluding the Co2+ sites, the as-derived Co sites with 3+ initial states exhibited intrinsically high OER activity, validating the effectiveness of the strategy of stabilizing high valence Co sites.

To Molecularly Block Hydrogen Evolution Sites of Molybdenum Disulfide toward Improved Catalytic Performance for Electrochemical Nitrogen Reduction.

2H-molybdenum disulfide (2H-MoS2 ) represents a classical catalyst for the electrochemical N2 reduction reaction (NRR) in water that offers a promising technology toward sustainable production of NH3 driven by renewable energy. While the catalytic efficiency is severely limited by a simultaneous and competing H2 evolution reaction (HER). Herein, it is proposed that the S edge of 2H-MoS2 , which is known as main sites to afford HER, is intentionally covered by cobalt phthalocyanine (CoPc) molecules through axial coordination. While the Mo sites with S vacancies at 2H-MoS2 edge is recognized as highly NRR active, and can keep structurally intact in the CoPc based modification. The resultant composite thus exhibits high NRR performance with Faradic efficiency and NH3 yields increase by fourfold and twofold, respectively, comparing to pristine 2H-MoS2 . These findings provide a deep insight into the mechanism of 2H-MoS2 based NRR catalysis and suggest an efficient molecular modification strategy to promote NRR in water.