Atomically dispersed catalysts refer to substrate-supported heterogeneous catalysts featuring one or a few active metal atoms that are separated from one another. They represent an important class of materials ranging from single-atom catalysts (SACs) and nanoparticles (NPs). While SACs and NPs have been extensively reported, catalysts featuring a few atoms with well-defined structures are poorly studied. The difficulty in synthesizing such structures has been a critical challenge. Here we report a facile photochemical method that produces catalytic centers consisting of two Ir metal cations, bridged by O and stably bound to a support. Direct evidence unambiguously supporting the dinuclear nature of the catalysts anchored on α-FeO is obtained by aberration-corrected scanning transmission electron microscopy (AC-STEM). Experimental and computational results further reveal that the threefold hollow binding sites on the OH-terminated surface of α-FeO anchor the catalysts to provide outstanding stability against detachment or aggregation. The resulting catalysts exhibit high activities toward HO photooxidation.

Development of the Li-O 2 battery as a practical energy storage technology has been underpinned by the lack of a stable electrolyte to enable reversible conversion between O 2 and Li 2 O 2 , given that previous applied organic electrolytes all show reactivity toward reactive oxygen species. Wang and colleagues show that this issue can be solved with a water-in-salt electrolyte that contains no organic solvent molecules. The net result is a highly effective electrolyte that enables stable Li-O 2 battery operations up to 300 cycles.

CO 2 electrochemical reduction is of great interest not only for its technological implications but also for the scientific challenges it represents. How to suppress the kinetically favored hydrogen evolution in the presence of H 2 O, for instance, has attracted significant attention. Here we report a new way of achieving such a goal. Our strategy involves a unique water-in-salt electrolyte system, where the H 2 O concentration can be greatly suppressed due to the strong solvation of the high-concentration salt. More importantly, the water-in-salt electrolyte offers an opportunity to tune the H 2 O concentration for electrokinetic studies of CO 2 reduction, a parameter of critical importance to the understanding of the detailed mechanisms but difficult to vary previously. Using Au as a model catalyst platform, we observed a zeroth-order dependence of the reaction rate on the H 2 O concentration, strongly suggesting that electron transfer, rather than concerted proton electron transfer, from the electrode to the adsorbed CO 2 is the rate-determining step. The results shed new light on the mechanistic understanding of CO 2 electrochemical reduction. Our approach is expected to be applicable to other catalyst systems, as well, which will offer a new dimension to mechanistic studies by tuning H 2 O concentrations.

Dual redox mediators (RMs) were introduced for Mg-O batteries. 1,4-Benzoquinone (BQ) facilitates the discharge with an overpotential reduction of 0.3 V. 5,10,15,20-Tetraphenyl-21H,23H-porphine cobalt(ii) (Co(ii)TPP) facilitates the recharge with an overpotential decrease of up to 0.3 V. Importantly, the two redox mediators are compatible in the same DMSO-based electrolyte.