Electrocatalysis: Nanoporous Nitrogen-Doped Graphene Oxide/Nickel Sulfide Composite Sheets Derived from a Metal-Organic Framework as an Efficient Electrocatalyst for Hydrogen and Oxygen Evolution (Adv. Funct. Mater. 33/2017)
In article number 1700451, Wolfgang Schuhmann, Roland A. Fischer, and co-workers report a hybrid material of nanoporous nitrogen-doped graphene oxide with nickel sulfide nanosheets (NGO/Ni7S6). The new material exhibits bifunctional catalytic activities for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with an excellent stability in alkaline electrolytes. This approach shows promise toward efficient and cost-effective electrocatalytic porous graphene composites.
Copper ions exchanged into zeolites are active for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia (NH3), but the low-temperature rate dependence on copper (Cu) volumetric density is inconsistent with reaction at single sites. We combine steady-state and transient kinetic measurements, x-ray absorption spectroscopy, and first-principles calculations to demonstrate that under reaction conditions, mobilized Cu ions can travel through zeolite windows and form transient ion pairs that participate in an oxygen (O2)–mediated CuI->CuII redox step integral to SCR. Electrostatic tethering to framework aluminum centers limits the volume that each ion can explore and thus its capacity to form an ion pair. The dynamic, reversible formation of multinuclear sites from mobilized single atoms represents a distinct phenomenon that falls outside the conventional boundaries of a heterogeneous or homogeneous catalyst.