Hydrophobic SiO2 Armor: Stabilizing Cuδ+ to Enhance CO2 Electroreduction toward C2+ Products in Strong Acidic Environments.

Electroreduction of CO2 in highly acidic environments holds promise for enhancing CO2 utilization efficiency. Due to the HER interference and structural instability, however, challenges in improving the selectivity and stability toward multicarbon (C2+) products remain. In this study, we proposed an "armor protection" strategy involving the deposition of ultrathin, hydrophobic SiO2 onto the Cu surface (Cu/SiO2) through a simple one-step hydrolysis. Our results confirmed the effective inhibition of HER by a hydrophobic SiO2 layer, leading to a high Faradaic efficiency (FE) of up to 76.9% for C2+ products at a current density of 900 mA cm-2 under a strongly acidic condition with a pH of 1. The observed high performance surpassed the reported performance for most previously studied Cu-based catalysts in acidic CO2RR systems. Furthermore, the ultrathin hydrophobic SiO2 shell was demonstrated to effectively prevent the structural reconstruction of Cu and preserve the oxidation state of Cuδ+ active sites during CO2RR. Additionally, it hindered the accumulation of K+ ions on the catalyst surface and diffusion of in situ generated OH- ions away from the electrode, thereby favoring C2+ product generation. In situ Raman analyses coupled with DFT simulations further elucidated that the SiO2 shell proficiently modulated *CO adsorption behavior on the Cu/SiO2 catalyst by reducing *CO adsorption energy, facilitating the C-C coupling. This work offers a compelling strategy for rationally designing and exploiting highly stable and active Cu-based catalysts for CO2RR in highly acidic environments.

Construction of Co-Se-W at Interfaces of Phase-Mixed Cobalt Selenide via Spontaneous Phase Transition for Platinum-Like Hydrogen Evolution Activity and Long-Term Durability in Alkaline and Acidic Media.

Cost-effective transition metal chalcogenides are highly promising electrocatalysts for both alkaline and acidic hydrogen evolution reactions (HER). However, unsatisfactory HER kinetics and stability have severely hindered their applications in industrial water electrolysis. Herein, a nanoflowers-shaped W-doped cubic/orthorhombic phase-mixed CoSe2 catalyst ((c/o)-CoSe2-W) is reported. The W doping induces spontaneous phase transition from stable phase cubic CoSe2 (c-CoSe2) to metastable phase orthorhombic CoSe2, which not only enables precise regulation of the ratio of two phases but also realizes W doping at the interfaces of two phases. The (c/o)-CoSe2-W catalyst exhibits a Pt-like HER activity in both alkaline and acidic media, with record-low HER overpotentials of 29.8 mV (alkaline) and 35.9 mV (acidic) at 10 mA cm-2, respectively, surpassing the vast majority of previously reported non-precious metal electrocatalysts for both alkaline and acidic HER. The Pt-like HER activities originate from the formation of Co-Se-W active species on the c-CoSe2 side at the phase interface, which effectively modulates electron structures of active sites, not only enhancing H2O adsorption and dissociation at Co sites but also optimizing H* adsorption to ΔGH* ≈ 0 at W sites. Benefiting from the abundant phase interfaces, the catalyst also displays outstanding long-term durability in both acidic and alkaline media.

Breaking the Activity and Stability Bottlenecks of Electrocatalysts for Oxygen Evolution Reactions in Acids.

Oxygen evolution reaction (OER) is a cornerstone reaction for a variety of electrochemical energy conversion and storage systems such as water splitting, CO2 /N2 reduction, reversible fuel cells, and metal-air batteries. However, OER catalysis in acids suffers from extra sluggish kinetics due to the additional step of water dissociation along with its multiple electron transfer processes. Furthermore, OER catalysts often suffer from poor stability in harsh acidic electrolytes due to the severe dissolution/corrosion processes. The development of active and stable OER catalysts in acids is highly demanded. Here,  the recent advances in OER electrocatalysis in acids are reviewed and the key strategies are summarized to overcome the bottlenecks of activity and stability for both noble-metal-based and noble metal-free catalysts, including i) morphology engineering, ii) composition engineering, and iii) defect engineering. Recent achievements in operando characterization and theoretical calculations are summarized which provide an unprecedented understanding of the OER mechanisms regarding active site identification, surface reconstruction, and degradation/dissolution pathways. Finally, views are offered on the current challenges and opportunities to break the activity-stability relationships for acidic OER in mechanism understanding, catalyst design, as well as standardized stability and activity evaluation for industrial applications such as proton exchange membrane water electrolyzers and beyond.

Achieving Highly Proton-Resistant Zn-Pb Anode through Low Hydrogen Affinity and Strong Bonding for Long-Life Electrolytic Zn//MnO2 Battery.

High-energy electrolytic Zn//MnO2 batteries show potential for grid-scale energy storage, but the severe hydrogen evolution corrosion (HEC) caused by acidic electrolytes results in subdued durability. Here, an all-around protection strategy is reported for achieving stable Zn metal anodes. First, a proton-resistant Pb-containing (Pb and Pb(OH)2 ) interface is constructed on a Zn anode (denoted as Zn@Pb), which in situ forms PbSO4 during H2 SO4 corrosion and protects the Zn substrate from HEC. Second, to improve the plating/stripping reversibility of Zn@Pb, Pb(CH3 COO)2 an additive (denoted as Zn@Pb-Ad) is introduced, which triggers PbSO4 precipitation and releases trace Pb2+ that can dynamically deposit a Pb layer on the Zn plating layer to suppress HEC. The superior HEC resistance stems from the low affinity of PbSO4 and Pb for H+ , as well as strong bonding between Pb-Zn or Pb-Pb, which increase the hydrogen evolution reaction overpotential and the H+ corrosion energy barrier. Consequently, the Zn@Pb-Ad//MnO2 battery runs stably for 630 and 795 h in 0.2 and 0.1 m H2 SO4 electrolytes, respectively, which are >40 times better than that of bare Zn. The as-prepared A h-level battery achieves a one-month calendar life, opening the door to the next generation of high-durable grid-scale Zn batteries.

High-Voltage-Enabled Stable Cobalt Species Deposition on MnO2 for Water Oxidation in Acid.

The design and maintenance of highly active sites in an acidic environment is vital and challenging for the oxygen evolution reaction (OER). In this work, it is found that the obtained CoO2 under high applied potential can be stable on MnO2 host in acidic environment, which may act as an effective means to solve the instability of cobalt-based electrocatalyst. The significant improvement of acidic OER activity (6.9 times) and stability (46.4 times) of 90-Co-MnO2 (treated by molten salt with more Co deposition sites) demonstrates the advantages of this approach. In situ Raman and the Pourbaix diagram suggest that the enhanced performance derives from the stable presence of CoO2 at the voltage >1.8 V versus reversible hydrogen electrode (RHE). However, when the potential is <1.8 V, the corresponding other cobalt species is too unstable to facilitate the OER. Density functional theorycalculations reveal that the deposited cobalt oxides can act as active sites, thus effectively reducing the reaction energy barrier of the rate-determining step. This work provides a new perspective for enhancing the stability of cobalt-based electrocatalyst. In the future, the dual consideration of applied potential and stable species of active element in the Pourbaix diagram may be a new direction for developing acid-stable electrocatalysts.

Black Phosphorous Mediates Surface Charge Redistribution of CoSe2 for Electrochemical H2 O2 Production in Acidic Electrolytes.

Electrochemical generation of hydrogen peroxide (H2 O2 ) by two-electron oxygen reduction offers a green method to mitigate the current dependence on the energy-intensive anthraquinone process, promising its on-site applications. Unfortunately, in alkaline environments, H2 O2 is not stable and undergoes rapid decomposition. Making H2 O2 in acidic electrolytes can prevent its decomposition, but choices of active, stable, and selective electrocatalysts are significantly limited. Here, the selective and efficient two-electron reduction of oxygen toward H2 O2 in acid by a composite catalyst that is composed of black phosphorus (BP) nailed chemically on the metallic cobalt diselenide (CoSe2 ) surface is reported. It is found that this catalyst exhibits a 91% Faradic efficiency for H2 O2 product at an overpotential of 300 mV. Moreover, it can mediate oxygen to H2 O2 with a high production rate of ≈1530 mg L-1 h-1 cm-2 in a flow-cell reactor. Spectroscopic and computational studies together uncover a BP-induced surface charge redistribution in CoSe2 , which leads to a favorable surface electronic structure that weakens the HOO* adsorption, thus enhancing the kinetics toward H2 O2 formation.

Efficient and Selective Electroreduction of CO2 to HCOOH over Bismuth-Based Bromide Perovskites in Acidic Electrolytes.

Metal halide perovskites, primarily used as optoelectronic devices, have not been applied for electrochemical conversion due to their insufficient stability in moisture. Herein, two bismuth-based perovskites are introduced as novel electrocatalysts to convert CO2 into HCOOH in aqueous acidic media (pH 2.5), exhibiting a high Faradaic efficiency for HCOOH of >80 % in a wide potential range from -0.75 to -1.25 V. Their structural evolution against water was dynamically monitored by in situ spectra. Theoretical calculations further reveal that the formation of intermediate OCHO* on bismuth sites of Cs3 Bi2 Br9 (111) play a pivotal role toward HCOOH production, which has a lower energy barrier than that on Cs2 AgBiBr6 (001) surfaces. Significantly, CO2 reacts with protons instead of water which can enhance CO2 reduction rate and suppress hydrogen evolution by avoiding carbonate formation in acidic electrolytes. This work paves the way for the extensive investigation of halide perovskites in aqueous systems.

Porous Fe5Si3 intermetallic anode for the oxygen evolution reaction in acidic electrolytes.

Here, we show that a reactive synthesis method of mixed elemental powders can be used to synthesize a porous electrode consisting of an intermetallic Fe5Si3 that exhibits catalytic activity towards oxygen evolution reaction (OER) in acidic solutions, which is capable of delivering 10 mA cm-2 at an overpotential of 0.73 V and a small Tafel slope of ~ 381.8 mV dec-1. The amorphous silica formed in the anode surface during the electrochemical process is multifunctional, as it protects the electrode substrate from corrosion and acts as electrocatalysts for OER. Remarkably, the Si-based intermetallics can be generalized to include other OER catalytic elements (Mn, Fe, Co), including Mn-Si and Co-Si intermetallics.

Bipolar Organic Polymer for High Performance Symmetric Aqueous Proton Battery.

Bipolar electroactive organic molecules receive an increasing research attention as electrode materials for rechargeable batteries due to their flexibility, controllability, and environmental friendliness. While its application for symmetric aqueous proton batteries is still in its infancy. Herein, a symmetric aqueous proton battery (APB) based on a bipolar poly(aminoanthraquinone) (PNAQ) is developed. The conductivity and solubility of PNAQ are significantly improved by introducing a polyaniline-like skeleton. It is demonstrated that the quinone-based moieties allow H+ reversible uptake/removal and the benzene ring-based units achieve HSO4 - adsorption/desorption. The fabricated symmetric APB exhibits a high discharge capacity of 85.3 mA h g-1 at 5 C and excellent rate performance (77 mA h g-1 at 100 C). The good rate performance benefits from capacitance-like ions diffusion mechanism. Furthermore, surprisingly, the system can also operate at -70 °C and shows superior electrochemical performance (60.4 mA h g-1 at -70 °C).

Robust Interface Ru Centers for High-Performance Acidic Oxygen Evolution.

RuO2 is considered as the state-of-the-art electrocatalyst for the oxygen evolution reaction (OER) in acidic media. However, its practical application is largely hindered by both the high reaction overpotential and severe electrochemical corrosion of the active centers. To overcome these limitations, innovative design strategies are necessary, which remains a great challenge. Herein, robust interface Ru centers between RuO2 and graphene, via a controllable oxidation of graphene encapsulating Ru nanoparticles, are presented to efficiently enhance both the activity and stability of the acidic OER. Through precisely controlling the reaction interface, a much lower OER overpotential of only 227 mV at 10 mA cm-2 in acidic electrolyte, compared with that of 290 mV for commercial RuO2 , but a significantly higher durability than the commercial RuO2 , are achieved. Density functional theory (DFT) calculations reveal that the interface Ru centers between the RuO2 and the graphene can break the classic scaling relationships between the free energies of HOO* and HO* to reduce the limiting potential, rendering an enhancement in the intrinsic OER activity and the resistance to over-oxidation and corrosion for RuO2 .

Fabricating an Aqueous Symmetric Supercapacitor with a Stable High Working Voltage of 2 V by Using an Alkaline-Acidic Electrolyte.

Aqueous symmetric carbon-based supercapacitors (CSCs) are always the research focus for energy storage devices because of the virtue of low cost, inherent safety, and encouraging electrochemical stability. As is well-known, so far most aqueous symmetric CSCs are subjected to low energy densities. Here, a symmetric supercapacitor comprising electrodes from biomass-derived activated carbon and alkaline-acidic electrolyte is reported. This aqueous symmetric CSC demonstrates exceptional electrochemical performance with high stable working voltage of 2 V and attractive cycling stability of no capacitance loss over 10 000 cycles. Impressively, it shows a remarkable energy density of 36.9 W h kg-1 at 248 W kg-1 based on the total mass of the active materials, which is much higher than traditional aqueous symmetric CSCs, and a power density of 4083 W kg-1 with an energy density of 8.8 W h kg-1. The use of stable alkaline-acidic electrolyte provides an innovative technique to enhance the energy density of aqueous supercapacitors.