Single-metal site catalysts have exhibited highly efficient electrocatalytic properties due to their unique coordination environments and adjustable local structures for reactant adsorption and electron transfer. They have been widely studied for many electrochemical reactions, including oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, it remains a significant challenge to realize high-efficiency bifunctional catalysis (ORR/OER) with single-metal-type active sites. Herein, we report atomically dispersed Fe–Co dual metal sites (FeCo–NC) derived from Fe and Co co-doped zeolitic imidazolate frameworks (ZIF-8s), aiming to build up multiple active sites for bifunctional ORR/OER catalysts. The atomically dispersed FeCo–NC catalyst shows excellent bifunctional catalytic activity in alkaline media for the ORR (E 1/2 = 0.877 V) and the OER (E j=10 = 1.579 V). Moreover, its outstanding stability during the ORR and the OER is comparable to noble-metal catalysts (Pt/C and RuO2). The atomic dispersion state, coordination structure, and the charge density difference of the dual metal site FeCo–NC were characterized and determined using advanced physical characterization and density functional theory (DFT) calculations. The FeCo–N6 moieties are likely the main active sites simultaneously for the ORR and the OER with improved performance relative to the traditional single Fe and Co site catalysts. We further incorporated the FeCo–NC catalyst into an air electrode for fabricating rechargeable and flexible Zn–air batteries, generating a superior power density (372 mW cm–2) and long-cycle (over 190 h) stability. This work would provide a method to design and synthesize atomically dispersed multi-metal site catalysts for advanced electrocatalysis.

Core Ideas Studying the critical zone requires targeted research on water, energy, gas, solutes, and sediments. The SSHCZO targets a 165‐km2 watershed on sedimentary rocks in the northeastern United States. One SSHCZO subcatchment, Shale Hills, provides extraordinary data describing a shale CZ. The Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) was established to investigate the form, function, and dynamics of the critical zone developed on sedimentary rocks in the Appalachian Mountains in central Pennsylvania. When first established, the SSHCZO encompassed only the Shale Hills catchment, a 0.08‐km2 subcatchment within Shaver's Creek watershed. The SSHCZO has now grown to include 120 km2 of the Shaver's Creek watershed. With that growth, the science team designed a strategy to measure a parsimonious set of data to characterize the critical zone in such a large watershed. This parsimonious design includes three targeted subcatchments (including the original Shale Hills), observations along the main stem of Shaver's Creek, and broad topographic and geophysical observations. Here we describe the goals, the implementation of measurements, and the major findings of the SSHCZO by emphasizing measurements of the main stem of Shaver's Creek as well as the original Shale Hills subcatchment.

Although dielectric energy-storing devices are frequently used in high voltage level, the fast growing on the portable and wearable electronics have been increasing the demand on the energy-storing devices at finite electric field strength. This paper proposes an approach on enhancing energy density under low electric field through compositionally inducing tricriticality in Ba(Ti,Sn)O3 ferroelectric material system with enlarged dielectric response. The optimal dielectric permittivity at tricritical point can reach to εr = 5.4 × 104, and the associated energy density goes to around 30 mJ/cm3 at the electric field of 10 kV/cm, which exceeds most of the selected ferroelectric materials at the same field strength. The microstructure nature for such a tricritical behavior shows polarization inhomogeneity in nanometeric scale, which indicates a large polarizability under external electric field. Further phenomenological Landau modeling suggests that large dielectric permittivity and energy density can be ascribed to the vanishing of energy barrier for polarization altering caused by tricriticality. Our results may shed light on developing energy-storing dielectrics with large permittivity and energy density at low electric field.

Core Ideas Two new subcatchments are used to test the importance of lithology and land use. Differences in lithology and land use result in differences in soils and waters. Despite differences, all catchments have a shallow and a deep water table. The relative importance of flow paths controls distinct chemistry response to discharge. Cross‐site comparison will ultimately enable upscaling from the catchment to large scale. The footprint of the Susquehanna Shale Hills Critical Zone Observatory was expanded in 2013 from the forested Shale Hills subcatchment (0.08 km2) to most of Shavers Creek watershed (163 km2) in an effort to understand the interactions among water, energy, gas, solute, and sediment. The main stem of Shavers Creek is now monitored, and instrumentation has been installed in two new subcatchments: Garner Run and Cole Farm. Garner Run is a pristine forested site underlain by sandstone, whereas Cole Farm is a cultivated site on calcareous shale. We describe preliminary data and insights about how the critical zone has evolved on sites of different lithology, vegetation, and land use. A notable conceptual model that has emerged is the “two water table” concept. Despite differences in critical zone architecture, we found evidence in each catchment of a shallow and a deep water table, with the former defined by shallow interflow and the latter defined by deeper groundwater flow through weathered and fractured bedrock. We show that the shallow and deep waters have distinct chemical signatures. The proportion of contribution from each water type to stream discharge plays a key role in determining how concentrations, including nutrients, vary as a function of stream discharge. This illustrates the benefits of the critical zone observatory approach: having common sites to grapple with cross‐disciplinary research questions, to integrate diverse datasets, and to support model development that ultimately enables the development of powerful conceptual and numerical frameworks for large‐scale hindcasting and forecasting capabilities.

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For photoelectrochemical (PEC) water splitting, the interface interactions among semiconductors, electrocatalysts, and electrolytes affect the charge separation and catalysis in turn. Here, through the changing of the bath temperature, Co-based oxygen evolution catalysts (OEC) with different crystallinities were electrochemically deposited on Ti-doped FeO (Ti-FeO) photoanodes. We found: (1) the OEC with low crystallinity is highly ion-permeable, decreasing the interactions between OEC and photoanode due to the intimate interaction between semiconductor and electrolyte; (2) the OEC with high crystallinity is nearly ion-impermeable, is beneficial to form a constant buried junction with semiconductor, and exhibits the low OEC catalytic activity; and (3) the OEC with moderate crystallinity is partially electrolyte-screened, thus contributing to the formation of ideal band bending underneath surface of semiconductor for charge separation and the highly electrocatalytic activity of OEC for lowering over-potentials of water oxidation. Our results demonstrate that to balance the water oxidation activity of OEC and OEC-semiconductor interface energetics is crucial for highly efficient solar energy conversion; in particular, the energy transducer is a semiconductor with a shallow or moderate valence-band level.

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