Perovskite oxides have attracted significant attention as energy conversion materials for metal-air battery and solid-oxide fuel-cell electrodes owing to their unique physical and electronic ...properties. Amongst these unique properties is the structural stability of the cation array in perovskites that can accommodate mobile oxygen ions under electrical polarization. Despite oxygen ion mobility and vacancies having been shown to play an important role in catalysis, their role in charge storage has yet to be explored. Herein we investigate the mechanism of oxygen-vacancy-mediated redox pseudocapacitance for a nanostructured lanthanum-based perovskite, LaMnO3. This is the first example of anion-based intercalation pseudocapacitance as well as the first time oxygen intercalation has been exploited for fast energy storage. Whereas previous pseudocapacitor and rechargeable battery charge storage studies have focused on cation intercalation, the anion-based mechanism presented here offers a new paradigm for electrochemical energy storage.
Urea electrooxidation has attracted considerable interest as an alternative anodic reaction in the electrochemical generation of hydrogen due to both the lower electrochemical potential required to ...drive the reaction and also the possibility of eliminating a potentially harmful substance from wastewater during hydrogen fuel production. Nickel and nickel-containing oxides have shown activities comparable to those of precious-metal catalysts for the electrooxidation of urea in alkaline conditions. Herein, we investigate the use of nanostructured LaNiO3 perovskite supported on Vulcan carbon XC-72 as an electrocatalyst. This catalyst exhibits an exceptionally high mass activity of ca. 371 mA mgox –1 and specific activity of 2.25 A mg–1 cmox –2 for the electrooxidation of urea in 1 M KOH, demonstrating the potential applications of Ni-based perovskites for direct urea fuel cells and low-energy hydrogen production. While LaNiO3 is shown to be stable at low overpotentials, through in-depth mechanistic studies the catalyst surface was observed to restructure and there was apparent CO2 poisoning of the LaNiO3 upon extended cycling, a result that may be extended to other Ni-based systems.
Perovskites are of great interest as replacements for precious metals and oxides used in bifunctional air electrodes involving the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). ...Herein, we report the synthesis and activity of a phase-pure nanocrystal perovskite catalyst that is highly active for the OER and ORR. The OER mass activity of LaNiO3, synthesized by the calcination of a rapidly dried nanoparticle dispersion and supported on nitrogen-doped carbon, is demonstrated to be nearly 3-fold that of 6 nm IrO2 and exhibits no hysteresis during oxygen evolution. Moreover, strong OER/ORR bifunctionality is shown by the low total overpotential (1.02 V) between the reactions, on par or better than that of noble metal catalysts such as Pt (1.16 V) and Ir (0.92 V). These results are examined in the context of surface hydroxylation, and a new OER cycle is proposed that unifies theory and the unique surface properties of LaNiO3.
Consumption of unsafe water is a major cause of morbidity and mortality in developing regions. Pasteurizing or boiling water to remove pathogens is energy‐intensive and often impractical to off‐grid ...communities. Therefore, low capital cost, rapid and energy‐efficient water disinfection methods are urgently required to address global challenges of safe water access. Here, anti‐bacterial hydrogels (ABHs) with catechol‐enabled molecular‐level hydrogen peroxide generators and quinone‐anchored activated carbon particles are designed for effective water treatment. The bactericidal effect is attributed to the synergy of hydrogen peroxide and quinone groups to attack essential cell components and disturb bacterial metabolism. ABHs can be directly used as tablets to achieve >99.999% water disinfection efficiency within 60 min without energy input. No harmful byproducts are formed during the treatment process, after which the ABH tablets can be easily removed without residues. Taking advantage of their excellent photothermal and biofouling‐resistant properties, ABHs can also be applied as solar evaporators to achieve stable water purification under sunlight (≤1 kW m−2) after months of storage and operation in bacteria‐containing river water. The ABH platform offers reduced energy and chemical demands for point‐of‐use water treatment technologies in remote areas and emergency rescue applications.
Antibacterial hydrogels (ABHs) are designed as tablets for rapid water disinfection (>99.999%) and can be easily removed from water without leaving chemical impurities. With excellent photothermal and biofouling‐resistant properties, ABHs can also be functional in solar water‐purification technologies to enable stable distillate production after months of storage and operation in bacteria‐containing river water.
The ability to design and characterize uniform, bimetallic alloy nanoparticles, where the less active metal enhances the activity of the more active metal, would be of broad interest in catalysis. ...Herein, we demonstrate that simultaneous reduction of Ag and Pd precursors provides uniform, Ag-rich AgPd alloy nanoparticles (∼5 nm) with high activities for the oxygen reduction reaction (ORR) in alkaline media. The particles are crystalline and uniformly alloyed, as shown by X-ray diffraction and probe corrected scanning transmission electron microscopy. The ORR mass activity per total metal was 60% higher for the AgPd2 alloy relative to pure Pd. The mass activities were 2.7 and 3.2 times higher for Ag9Pd (340 mA/mgmetal) and Ag4Pd (598 mA/mgmetal), respectively, than those expected for a linear combination of mass activities of Ag (60 mA/mgAg) and Pd (799 mA/mgPd) particles, based on rotating disk voltammetry. Moreover, these synergy factors reached 5-fold on a Pd mass basis. For silver-rich alloys (Ag≥4Pd), the particle surface is shown to contain single Pd atoms surrounded by Ag from cyclic voltammetry and CO stripping measurements. This morphology is favorable for the high activity through a combination of modified electronic structure, as shown by XPS, and ensemble effects, which facilitate the steps of oxygen bond breaking and desorption for the ORR. This concept of tuning the heteroatomic interactions on the surface of small nanoparticles with low concentrations of precious metals for high synergy in catalytic activity may be expected to be applicable to a wide variety of nanoalloys.
Interfacial solar vapor generation (SVG) is regarded as a promising and sustainable strategy for clean water production. While many materials have demonstrated excellent evaporation rates under one ...sun, it remains challenging to design solar evaporators without compromising SVG performance in high‐salinity brines (≥10 wt %). Herein, polyzwitterionic hydrogels (PZHs) are proposed as a novel platform for high‐salinity solar desalination. Taking advantage of the unique anti‐polyelectrolyte effects, PZHs can trap salt ions from the brine water to form a more hydrated polymer network, leading to enhanced SVG performance. PZHs exhibit an exceptional solar evaporation rate of 4.14 kg m−2 h−1 in 10 wt % brine, which is ≈20 % higher than that in pure water. It is anticipated that salt‐responsive PZHs may provide insights for the design of next‐generation solar desalination systems.
A novel polyzwitterionic hydrogel as highly efficient solar evaporator is developed for high‐salinity solar desalination. The hydrogel evaporator could achieve a rapid solar evaporation rate of 4.14 kg m−2 h−1 with high energy efficiency (≈94 %) in 10 wt % brine. This polyzwitterionic hydrogel offers insight to design next‐generation solar evaporators for high‐salinity brine.
Abstract
Hydrogel‐based evaporators for interfacial solar vapor generation (SVG) have emerged as a promising and sustainable strategy for freshwater production. Nevertheless, developing a green and ...simple approach in the fabrication of porous hydrogel‐based evaporators with tunable porous structures and superior mechanical properties continues to be a challenge. Herein, cryo‐assembled templating and polymerization (CTP) is proposed as an ecological, simple yet effective approach to synthesizing sponge‐like hydrogels (SPHs) with outstanding mechanical properties. Moreover, inspired by the structural geometry of conifer plants of radially aligned microchannels and vertical vessels granting impressive water transportation abilities, the polyzwitterionic SPH evaporators with biomimetically assembled structure (B‐SPH) raise the water transport rate by up to nearly 2 orders of magnitude compared to bulk hydrogels. The B‐SPH also enables an SVG rate up to ≈ 3.45 kg m
−2
h
−1
under one sun irradiation and an energy efficiency of ≈ 95%. In addition, the as‐prepared materials feature stable mechanical properties and SVG performance even after being rolled, folded, and twisted over hundred times. It is anticipated that the B‐SPH prepared by CTP method provides insights into scalable hydrogel‐based evaporators with elaborate porous structures and durable mechanical properties in an energy‐efficient manner.
We present a series of perovskite electrocatalysts that are highly active for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in an aqueous alkaline electrolyte. ...Lanthanum-based perovskites containing different transition metal active sites (LaBO3, B = Ni, Ni0.75Fe0.25, Co, Mn) are synthesized by a general colloidal method, yielding phase pure catalysts of homogeneous morphology and surface area (8–14 m2/g). Each perovskite’s ability to catalyze the OER and ORR is examined using thin film rotating disk electrochemistry (RDE). LaCoO3 supported on nitrogen-doped carbon is shown to be ∼3 times more active for the OER than high-surface-area IrO2. Furthermore, LaCoO3 is demonstrated to be highly bifunctional by having a lower total overpotential between the OER and ORR (ΔE = 1.00 V) than Pt (ΔE = 1.16) and Ru (ΔE = 1.01). The OER and ORR pathways are perturbed by the introduction of peroxide disproportionation functionality via support interactions and selective doping of the catalyst. LaNi0.75Fe0.25O3’s ability to disproportionate peroxide is hypothesized to be responsible for the ∼50% improvement over LaNiO3 in catalytic activity toward the ORR, despite similar electronic structure. These results allow us to examine the pathways for OER and ORR in context of support interactions, transition metal redox processes, and catalytic bifunctionality.
Interfacial evaporation using porous hydrogels has demonstrated highly effective solar evaporation performance under natural sunlight to ensure an affordable clean water supply. However, it remains ...challenging to realize scalable and ready‐to‐use hydrogel materials with durable mechanical properties. Here, self‐assembled templating (SAT) is developed as a simple yet effective method to fabricate large‐scale elastic hydrogel evaporators with excellent desalination performance. The highly interconnected porous structure of the hydrogels with low tortuosity and tunable pore size enables high level of tunability on the water transport rate. With superior elasticity, the porous hydrogels are easy to process with a rapid shape recovery after being rolled, folded, and twisted over hundred times, and exhibit highly effective and stable evaporation with an evaporation rate of ≈2.8 kg m−2 h−1 and ≈90 % solar‐to‐vapor efficiency. It is anticipated that this SAT strategy, without the typical need for freeze‐drying, will accelerate the industrialization of hydrogel solar evaporators for practical applications.
A simple yet effective method, self‐assembled templating (SAT), is developed to synthesize 3D large‐scale, highly interconnected porous hydrogels (IPH). IPHs exhibit rapid water transport ability, quick shape recovery, and durable mechanical features, showing a promising method to scale up hydrogel solar evaporators for practical clean water production.
Abstract
Perovskite oxides are attractive candidates as catalysts for the electrolysis of water in alkaline energy storage and conversion systems. However, the rational design of active catalysts has ...been hampered by the lack of understanding of the mechanism of water electrolysis on perovskite surfaces. Key parameters that have been overlooked include the role of oxygen vacancies, B–O bond covalency, and redox activity of lattice oxygen species. Here we present a series of cobaltite perovskites where the covalency of the Co–O bond and the concentration of oxygen vacancies are controlled through Sr
2+
substitution into La
1−
x
Sr
x
CoO
3−
δ
. We attempt to rationalize the high activities of La
1−
x
Sr
x
CoO
3−
δ
through the electronic structure and participation of lattice oxygen in the mechanism of water electrolysis as revealed through
ab initio
modelling. Using this approach, we report a material, SrCoO
2.7
, with a high, room temperature-specific activity and mass activity towards alkaline water electrolysis.
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