Low Ruthenium Content Confined on Boron Carbon Nitride as an Efficient and Stable Electrocatalyst for Acidic Oxygen Evolution Reaction

Amorphous MnRuOx Containing Microcrystalline for Enhanced Acidic Oxygen-Evolution Activity and Stability

Compared to Ir, Ru-based catalysts often exhibited higher activity but suffered significant and rapid activity loss during the challenging oxygen evolution reaction (OER) in a corrosive acidic environment. Herein, we developed a hybrid MnRuOx catalyst in which the RuO2 microcrystalline regions serve as a supporting framework, and the amorphous MnRuOx phase fills the microcrystalline interstices. In particular, the MnRuOx-300 catalyst from an annealing temperature of 300 °C contains an optimal amorphous/crystalline heterostructure, providing substantial defects and active sites, facilitating efficient adsorption and conversion of OH-. In addition, the heterostructure leads to a relative increase of the d-band center close to the Fermin level, thus accelerating electron transfer with reduced charge transfer resistance at the active interface between crystalline and amorphous phases during the OER. The catalyst was further thoroughly evaluated under various operating conditions and demonstrated exceptional activity and stability for the OER, representing a promising solution to replace Ir in water electrolyzers.

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

Ensuring high catalytic activity and durability at low iridium (Ir)usage is still a big challenge for the development of electrocatalysts toward 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). 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 differential electrochemical mass spectrometry, activation energy analysis and theoretical 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. The optimized catalyst delivers the excellent performance (1.85 V/3.0 A cm-2@80 °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) in PEMWE with low Ir usage of ≈0.4 mg cm-2, realizing the dramatical reduction of hydrogen (H2) production cost to 0.88 dollar per kg (H2).

Iron, Tungsten Dual-Doped Nickel Sulfide as Efficient Bifunctional Catalyst for Overall Water Splitting

Developing low-cost and highly efficient bifunctional catalysts for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is a challenging problem in electrochemical overall water splitting. Here, iron, tungsten dual-doped nickel sulfide catalyst (Fe/W-Ni3S2) is synthesized on the nickel foam, and it exhibits excellent OER and HER performance. As a result, the water electrolyze based on Fe/W-Ni3S2 bifunctional catalyst illustrates 10 mA cm-2 at 1.69 V (without iR-compensation) and highly durable overall water splitting over 100 h tested under 500 mA cm-2. Experimental results and DFT calculations indicate that the synergistic interaction between Fe doping and Ni vacancy induced by W leaching during the in situ oxidation process can maximize exposed OER active sites on the reconstructed NiOOH species for accelerating OER kinetics, while the Fe/W dual-doping optimizes the electronic structure of Fe/W-Ni3S2 and the binding strength of intermediates for boosting HER. This study unlocks the different promoting mechanisms of incorporating Fe and W for boosting the OER and HER activity of Ni3S2 for water splitting, which provides significant guidance for designing high-performance bifunctional catalysts for overall water splitting.

Weak-Field Electro-Flash Induced Asymmetric Catalytic Sites toward Efficient Solar Hydrogen Peroxide Production

Borocarbonitride (BCN), in a mesoscopic asymmetric state, is regarded as a promising photocatalyst for artificial photosynthesis. However, BCN materials reported in the literature primarily consist of symmetric N-[B]3 units, which generate highly spatial coupled electron-hole pairs upon irradiation, thus kinetically suppressing the solar-to-chemical conversion efficiency. Here, we propose a facile and fast weak-field electro-flash strategy, with which structural symmetry breaking is introduced on key nitrogen sites. As-obtained double-substituted BCN (ds-BCN) possesses high-concentration asymmetric [B]2-N-C coordination, which displays a highly separated electron-hole state and broad visible-light harvesting, as well as provides electron-rich N sites for O2 affinity. Thereby, ds-BCN delivers an apparent quantum yield of 7.6% at 400 nm and a solar-to-chemical conversion efficiency of 0.3% for selective 2e-reduction of O2 to H2O2, over 4-fold higher than that of the traditional calcined BCN analogue and superior to the metal-free C3N4-based photocatalysts reported so far. The weak-field electro-flash method and as-induced catalytic site symmetry-breaking methodologically provide a new method for the fast and low-cost fabrication of efficient nonmetallic catalysts toward solar-to-chemical conversions.

FeCoCuMnRuB Nanobox with Dual Driving of High-Entropy and Electron-Trap Effects as the Efficient Electrocatalyst for Water Oxidation

High-entropy borides hold potential as electrocatalysts for water oxidation. However, the synthesis of the tailored nanostructures remains a challenge due to the thermodynamic immiscibility of polymetallic components. Herein, a FeCoCuMnRuB nanobox decorated with a nanosheet array was synthesized for the first time by a "coordination-etch-reduction" method. The FeCoCuMnRuB nanobox has various structural characteristics to express the catalytic performance; meanwhile, it combines the high-entropy effect of multiple components with the electron trap effect induced by electron-deficient B, synergistically regulating its electronic structure. As a result, FeCoCuMnRuB nanobox exhibits enhanced OER activity with a low overpotential (η10 = 233 mV), high TOF value (0.0539 s-1), small Tafel slope (61 mV/dec), and a satisfactory stability for 200 h, outperforming the high-entropy alloy and low-entropy borides. This work develops a high entropy and electron-deficient B-driven strategy for motivating the catalytic performance of water oxidation, which broadens the structural diversity and category of high-entropy materials.

Efficient Acidic Photoelectrochemical Water Splitting Enabled by Ru Single Atoms Anchored on Hematite Photoanodes

Photoelectrochemical (PEC) water splitting in acidic media holds promise as an efficient approach to renewable hydrogen production. However, the development of highly active and stable photoanodes under acidic conditions remains a significant challenge. Herein, we demonstrate the remarkable water oxidation performance of Ru single atom decorated hematite (Fe2O3) photoanodes, resulting in a high photocurrent of 1.42 mA cm-2 at 1.23 VRHE under acidic conditions. Comprehensive experimental and theoretical investigations shed light on the mechanisms underlying the superior activity of the Ru-decorated photoanode. The presence of single Ru atoms enhances the separation and transfer of photogenerated carriers, facilitating efficient water oxidation kinetics on the Fe2O3 surface. This is achieved by creating additional energy levels within the Fe2O3 bandgap and optimizing the free adsorption energy of intermediates. These modifications effectively lower the energy barrier of the rate-determining step for water splitting, thereby promoting efficient PEC hydrogen production.

Enhanced Metal-Support Interactions Boost the Electrocatalytic Water Splitting of Supported Ruthenium Nanoparticles on a Ni3 N/NiO Heterojunction at Industrial Current Density

Developing highly efficient and stable hydrogen production catalysts for electrochemical water splitting (EWS) at industrial current densities remains a great challenge. Herein, we proposed a heterostructure-induced-strategy to optimize the metal-support interaction (MSI) and the EWS activity of Ru-Ni3 N/NiO. Density functional theory (DFT) calculations firstly predicted that the Ni3 N/NiO-heterostructures can improve the structural stability, electronic distributions, and orbital coupling of Ru-Ni3 N/NiO compared to Ru-Ni3 N and Ru-NiO, which accordingly decreases energy barriers and increases the electroactivity for EWS. As a proof-of-concept, the Ru-Ni3 N/NiO catalyst with a 2D Ni3 N/NiO-heterostructures nanosheet array, uniformly dispersed Ru nanoparticles, and strong MSI, was successfully constructed in the experiment, which exhibited excellent HER and OER activity with overpotentials of 190 mV and 385 mV at 1000 mA cm-2 , respectively. Furthermore, the Ru-Ni3 N/NiO-based EWS device can realize an industrial current density (1000 mA cm-2 ) at 1.74 V and 1.80 V under alkaline pure water and seawater conditions, respectively. Additionally, it also achieves a high durability of 1000 h (@ 500 mA cm-2 ) in alkaline pure water.