Synchronized conversion of CO2 and H2O into hydrocarbons and oxygen via infrared-ignited photocatalysis remains a challenge. Herein, the hydroxyl-coordinated single-site Ru is anchored precisely on the metallic TiN surface by a NaBH4/NaOH reforming method to construct an infrared-responsive HO-Ru/TiN photocatalyst. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (ac-HAADF-STEM) and X-ray absorption spectroscopy (XAS) confirm the atomic distribution of the Ru species. XAS and density functional theory (DFT) calculations unveil the formation of surface HO-RuN5-Ti Lewis pair sites, which achieves efficient CO2 polarization/activation via dual coordination with the C and O atoms of CO2 on HO-Ru/TiN. Also, implanting the Ru species on the TiN surface powerfully boosts the separation and transfer of photoinduced charges. Under infrared irradiation, the HO-Ru/TiN catalyst shows a superior CO2-to-CO transformation activity coupled with H2O oxidation to release O2, and the CO2 reduction rate can further be promoted by about 3-fold under simulated sunlight. With the key reaction intermediates determined by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and predicted by DFT simulations, a possible photoredox mechanism of the CO2 reduction system is proposed.

Hydroxyl-Bonded Ru on Metallic TiN Surface Catalyzing CO2 Reduction with H2O by Infrared Light.

The limited availability of freshwater in renewable energy-rich areas has led to the exploration of seawater electrolysis for green hydrogen production. However, the complex composition of seawater presents substantial challenges such as electrode corrosion and electrolyzer failure, calling into question the technological and economic feasibility of direct seawater splitting. Despite many efforts, a comprehensive overview and analysis of seawater electrolysis, including electrochemical fundamentals, materials, and technologies of recent breakthroughs, is still lacking. In this review, we systematically examine recent advances in electrocatalytic seawater splitting and critically evaluate the obstacles to optimizing water supply, materials, and devices for stable hydrogen production from seawater. We demonstrate that robust materials and innovative technologies, especially selective catalysts and high-performance devices, are critical for efficient seawater electrolysis. We then outline and discuss future directions that could advance the techno-economic feasibility of this emerging field, providing a roadmap toward the design and commercialization of materials that can enable efficient, cost-effective, and sustainable seawater electrolysis.

Emerging materials and technologies for electrocatalytic seawater splitting

Hexavalent iridium (IrVI) oxide is predicted to be more active and stable than any other iridium oxide for the oxygen evolution reaction in acid; however, its experimental realization remains challenging. In this work, we report the synthesis, characterization, and application of atomically dispersed IrVI oxide (IrVI-ado) for proton exchange membrane (PEM) water electrolysis. The IrVI-ado was synthesized by oxidatively substituting the ligands of potassium hexachloroiridate(IV) (K2IrCl6) with manganese oxide (MnO2). The mass-specific activity (1.7 × 105 amperes per gram of iridium) and turnover number (1.5 × 108) exceeded those of benchmark iridium oxides, and in situ x-ray analysis during PEM operations manifested the durability of IrVI at current densities up to 2.3 amperes per square centimeter. The high activity and stability of IrVI-ado showcase its promise as an anode material for PEM electrolysis. Editor’s summary Electrolytic water splitting to generate hydrogen is most commonly carried out under basic conditions. Major research efforts are being directed toward switching to the more efficient acidic conditions in a proton-exchange membrane (PEM) apparatus, but catalyst stability and expense remain serious obstacles. Li et al. report a means of oxidizing iridium catalysts to the +6 oxidation state using manganese oxide as the oxidant. The resultant iridium(VI) oxide proved highly active and stable over several months of continuous PEM testing, consistent with prior modeling predictions. —Jake S. Yeston

Atomically dispersed hexavalent iridium oxide from MnO2 reduction for oxygen evolution catalysis

Efficient oxygen evolution reaction electrocatalysts are essential for sustainable clean energy conversion. However, catalytic materials followed the conventional adsorbate evolution mechanism (AEM) with the inherent scaling relationship between key oxygen intermediates *OOH and *OH, or the lattice-oxygen-mediated mechanism (LOM) with the possible lattice oxygen migration and structural reconstruction, which are not favorable to the balance between high activity and stability. Herein, we propose an unconventional Co-Fe dual-site segmentally synergistic mechanism (DSSM) for single-domain ferromagnetic catalyst CoFeSx nanoclusters on carbon nanotubes (CNT) (CFS-ACs/CNT), which can effectively break the scaling relationship without sacrificing stability. Co3+ (L.S, t2g6eg0) supplies the strongest OH* adsorption energy, while Fe3+ (M.S, t2g4eg1) exposes strong O* adsorption. These dual-sites synergistically produce of Co-O-O-Fe intermediates, thereby accelerating the release of triplet-state oxygen ( ↑ O = O ↑ ). As predicted, the prepared CFS-ACs/CNT catalyst exhibits less overpotential than that of commercial IrO2, as well as approximately 633 h of stability without significant potential loss. 

Dual-site segmentally synergistic catalysis mechanism: boosting CoFeSx nanocluster for sustainable water oxidation

Ensuring high catalytic activity and durability at low Ir usage is still a big challenge for the development of electrocatalysts towards oxygen evolution reaction (OER) in proton exchange membrane water electrolysis (PEMWE). Here, a rapid liquid-reduction combined with surface galvanic replacement strategy is reported to synthesize the sub 2 nm high-entropy alloy (HEA) nanoparticles featured with Ir-rich IrRuNiMo medium-entropy oxide shell (Ir-MEO) and a IrRuCoNiMo HEA core (HEA@Ir-MEO), which exhibits a low overpotential of 243 mV at 10 mA cm-2 and high mass activity (261.5 A gIr -1). Advanced spectroscopies reveal that the Ir-rich MEO shell inhibits the severe structural evolution of transition metals upon the OER, thus guaranteeing the structural stability. In-situ DEMS, activation energy analysis and DFT calculations unveil that the OER on HEA@Ir-MEO follows an adsorbate evolution mechanism pathway, where the energy barrier of rate-determining step is substantially lowered, interpreting the enhanced OER kinetics. The optimized catalyst is assembled into PEM electrolyzer with low Ir usage of ca. 0.4 mg cm-2, and to give the excellent performance (1.85 V/3.0 A cm-2 °C), long-term stability (>500 h@1.0 Acm-2) and low energy consumption (3.98 kWh Nm-3 H2 @1.0 A cm-2), realizing the dramatical reduction of hydrogen production cost to USD 0.88 per kg H2. This article is protected by copyright. All rights reserved.

Sub-2 nm IrRuNiMoCo High-Entropy Alloy with Ir-Rich Medium-Entropy Oxide Shell to Boost Acidic Oxygen Evolution.

The trade-off between activity and stability of oxygen evolution reaction (OER) catalysts in proton exchange membrane water electrolyzer (PEMWE) is challenging. Crystalline IrO2 displays good stability but exhibits poor activity; amorphous IrOx exhibits outstanding activity while sacrificing stability. Here, we combine the advantages of these two materials via a lattice water–incorporated iridium oxide (IrOx·nH2O) that has short-range ordered structure of hollandite-like framework. We confirm that IrOx·nH2O exhibits boosted activity and ultrahigh stability of >5700 hours (~8 months) with a record-high stability number of 1.9 × 107 noxygen nIr−1. We evidence that lattice water is active oxygen species in sustainable and rapid oxygen exchange. The lattice water–assisted modified OER mechanism contributes to improved activity and concurrent stability with no apparent structural degradation, which is different to the conventional adsorbate evolution mechanism and lattice oxygen mechanism. We demonstrate that a high-performance PEMWE with IrOx·nH2O as anode electrocatalyst delivers a cell voltage of 1.77 V at 1 A cm−2 for 600 hours (60°C).

https://www.science.org/doi/pdf/10.1126/sciadv.adh1718?download=true

IrOx·nH2O with lattice water–assisted oxygen exchange for high-performance proton exchange membrane water electrolyzers

In this paper, three-ecofriendly reduced graphene oxides (rGOs) were obtained by using three green reducing agents (beer, wine and cocoa) to reduce the graphene oxide (GO), and were labeled as B-rGO, W-rGO and C-rGO. Meanwhile, rGO nanofluids with different water–ethanol volume ratios (25 : 75, 50 : 50, 75 : 25) were prepared based on three-ecofriendly rGOs. The structure properties of the three-ecofriendly rGOs were investigated by XRD, FR-IT, Raman spectroscopy and XPS analysis. Meanwhile, the thermophysical properties of rGO nanofluids were analyzed. Experimental results indicated that the stability and thermophysical properties of rGO nanofluids were slightly different, indicating that the properties of the nanofluids are dependent on the type of base fluids and nanoparticles. When the water–ethanol volume ratio was maintained at 25 : 75, the stability experiment results showed that W-rGO nanofluids presented excellent stability, which indirectly confirmed their excellent thermal conductivity. Furthermore, the contact angle experiment indicated that the contact angles of rGO nanofluids decreased with the increase of temperature. In a word, these three rGOs and their nanofluids exhibited preferable properties that make them promising in the field of heat transfer.

/pdf/characteristic-analysis-of-three-ecofriendly-reduced-3ol0xooo.pdf

Characteristic analysis of three-ecofriendly reduced graphene oxides (rGOs) and their application in water–ethanol-based fluids with different volume ratios

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IrOx·nH2O with lattice water–assisted oxygen exchange for high-performance proton exchange membrane water electrolyzers

Characteristic analysis of three-ecofriendly reduced graphene oxides (rGOs) and their application in water–ethanol-based fluids with different volume ratios