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Efficient hydrogen storage and release are essential for effective use of hydrogen as an energy carrier. In principle, formic acid could be used as a convenient hydrogen storage medium via reversible CO 2 hydrogenation. However, noble metal-based catalysts are currently needed to facilitate the (de)hydrogenation, and the CO 2 produced during hydrogen release is generally released, resulting in undesirable emissions. Here we report an α -amino acid-promoted system for reversible CO 2 hydrogenation to formic acid using a Mn-pincer complex as a homogeneous catalyst. We observe good stability and reusability of the catalyst and lysine as the amino acid at high productivities (CO 2 hydrogenation: total turnover number of 2,000,000; formic acid dehydrogenation: total turnover number of 600,000). Employing potassium lysinate, we achieve >80% H 2 evolution efficiency and >99.9% CO 2 retention in ten charge–discharge cycles, avoiding CO 2 re-loading steps between each cycle. This process was scaled up by a factor of 18 without obvious drop of the productivity. Formic acid is a convenient hydrogen storage medium with storage release occurring via reversible hydrogenation of CO 2 and facilitated by noble metal-based catalysts. Now, reversible storage release is demonstrated using a non-noble, Mn-based catalyst in the presence of an amino acid.

Improving the catalytic efficiency of platinum for the hydrogen evolution reaction is valuable for water splitting technologies. Hydrogen spillover has emerged as a new strategy in designing binary-component Pt/support electrocatalysts. However, such binary catalysts often suffer from a long reaction pathway, undesirable interfacial barrier, and complicated synthetic processes. Here we report a single-phase complex oxide La 2 Sr 2 PtO 7+δ as a high-performance hydrogen evolution electrocatalyst in acidic media utilizing an atomic-scale hydrogen spillover effect between multifunctional catalytic sites. With insights from comprehensive experiments and theoretical calculations, the overall hydrogen evolution pathway proceeds along three steps: fast proton adsorption on O site, facile hydrogen migration from O site to Pt site via thermoneutral La-Pt bridge site serving as the mediator, and favorable H 2 desorption on Pt site. Benefiting from this catalytic process, the resulting La 2 Sr 2 PtO 7+δ exhibits a low overpotential of 13 mV at 10 mA cm −2 , a small Tafel slope of 22 mV dec −1 , an enhanced intrinsic activity, and a greater durability than commercial Pt black catalyst. While renewable H 2 production offers a promising route for clean energy production, there is an urgent need to improve catalyst performances. Here, authors design a Pt-containing complex oxide that utilizes atomic-scale hydrogen spillover to promote H 2 evolution electrocatalysis in acidic media.

Solar-driven hydrogen production from water using particulate photocatalysts is considered the most economical and effective approach to produce hydrogen fuel with little environmental concern. However, the efficiency of hydrogen production from water in particulate photocatalysis systems is still low. Here, we propose an efficient biphase photocatalytic system composed of integrated photothermal–photocatalytic materials that use charred wood substrates to convert liquid water to water steam, simultaneously splitting hydrogen under light illumination without additional energy. The photothermal–photocatalytic system exhibits biphase interfaces of photothermally-generated steam/photocatalyst/hydrogen, which significantly reduce the interface barrier and drastically lower the transport resistance of the hydrogen gas by nearly two orders of magnitude. In this work, an impressive hydrogen production rate up to 220.74 μmol h −1  cm −2 in the particulate photocatalytic systems has been achieved based on the wood/CoO system, demonstrating that the photothermal–photocatalytic biphase system is cost-effective and greatly advantageous for practical applications. The solar-driven H 2 production from water by particulate photocatalysts is an effective approach to produce H 2 fuel. Here, the authors propose an integrated photothermal–photocatalytic biphase system, which lowers the reaction barrier and the delivery resistance of the H 2 , boosting the catalytic H 2 evolution rate.

Single-atom catalysts anchoring offers a desirable pathway for efficiency maximization and cost-saving for photocatalytic hydrogen evolution. However, the single-atoms loading amount is always within 0.5% in most of the reported due to the agglomeration at higher loading concentrations. In this work, the highly dispersed and large loading amount (>1 wt%) of copper single-atoms were achieved on TiO 2 , exhibiting the H 2 evolution rate of 101.7 mmol g −1  h −1 under simulated solar light irradiation, which is higher than other photocatalysts reported, in addition to the excellent stability as proved after storing 380 days. More importantly, it exhibits an apparent quantum efficiency of 56% at 365 nm, a significant breakthrough in this field. The highly dispersed and large amount of Cu single-atoms incorporation on TiO 2 enables the efficient electron transfer via Cu 2+ -Cu + process. The present approach paves the way to design advanced materials for remarkable photocatalytic activity and durability. In this work, the highly dispersed and large loading amount (>1 wt%) of copper single-atoms were achieved on TiO 2 , resulting into an apparent quantum efficiency of 56% at 365 nm, in addition to an excellent thermal stability as proved after storing 380 days.

Electrochemical saline water electrolysis using renewable energy as input is a highly desirable and sustainable method for the mass production of green hydrogen 1 – 7 ; however, its practical viability is seriously challenged by insufficient durability because of the electrode side reactions and corrosion issues arising from the complex components of seawater. Although catalyst engineering using polyanion coatings to suppress corrosion by chloride ions or creating highly selective electrocatalysts has been extensively exploited with modest success, it is still far from satisfactory for practical applications 8 – 14 . Indirect seawater splitting by using a pre-desalination process can avoid side-reaction and corrosion problems 15 – 21 , but it requires additional energy input, making it economically less attractive. In addition, the independent bulky desalination system makes seawater electrolysis systems less flexible in terms of size. Here we propose a direct seawater electrolysis method for hydrogen production that radically addresses the side-reaction and corrosion problems. A demonstration system was stably operated at a current density of 250 milliamperes per square centimetre for over 3,200 hours under practical application conditions without failure. This strategy realizes efficient, size-flexible and scalable direct seawater electrolysis in a way similar to freshwater splitting without a notable increase in operation cost, and has high potential for practical application. Importantly, this configuration and mechanism promises further applications in simultaneous water-based effluent treatment and resource recovery and hydrogen generation in one step. An efficient and scalable direct seawater electrolysis method for hydrogen production that addresses the side-reaction and corrosion problems associated with using seawater instead of pure water is demonstrated.

Designing efficient catalysts and understanding the underlying mechanisms for anodic nucleophile electrooxidation are central to the advancement of electrochemically-driven technologies. Here, a heterostructure of nickel boride/nickel catalyst is developed to enable methanol electrooxidation into formate with a Faradaic efficiency of nearly 100%. Operando electrochemical impedance spectroscopy and in situ Raman spectroscopy are applied to understand the influence of methanol concentration in the methanol oxidation reaction. High concentrations of methanol inhibit the phase transition of the electrocatalyst to high-valent electro-oxidation products, and electrophilic oxygen species (O* or OH*) formed on the electrocatalyst are considered to be the catalytically active species. Additional mechanistic investigation with density functional theory calculations reveals that the potential-determining step, the formation of *CH 2 O, occurs most favorably on the nickel boride/nickel heterostructure rather than on nickel boride and nickel. These results are highly instructive for the study of other nucleophile-based approaches to electrooxidation reactions and organic electrosynthesis. Understanding the role of active sites in electrooxidation reactions is important yet challenging. Here, the authors use operando spectroscopies to monitor the effect of methanol concentration on Ni 3 B/Ni heterostructures during formate production.

Amorphous semiconductors without perfect crystalline lattice structures are usually considered to be unfavorable for photocatalysis due to the presence of enriched trap states and defects. Here we demonstrate that breaking long-range atomic order in an amorphous ZnCdS photocatalyst can induce dipole moments and generate strong electric fields within the particles which facilitates charge separation and transfer. Loading 1 wt.% of low-cost Co-MoS x cocatalysts to the ZnCdS material increases the H 2 evolution rate to 70.13 mmol g −1 h −1 , which is over 5 times higher than its crystalline counterpart and is stable over the long-term up to 160 h. A flexible 20 cm × 20 cm Co-MoS x /ZnCdS film is prepared by a facile blade-coating technique and can generate numerous observable H 2 bubbles under natural sunlight, exhibiting potential for scale-up solar H 2 production. The rapid recombination of photogenerated charge carriers is a key challenge for photocatalytic hydrogen production. Here, the authors report an amorphous ZnCdS to break the symmetry of atom arrangement that induces strong dipole fields, thus providing extra driving forces for charge separation.

Efficient water electrolyzers are constrained by the lack of low-cost and earth-abundant hydrogen evolution reaction (HER) catalysts that can operate at industry-level conditions and be prepared with a facile process. Here we report a self-standing MoC–Mo 2 C catalytic electrode prepared via a one-step electro-carbiding approach using CO 2 as the feedstock. The outstanding HER performances of the MoC–Mo 2 C electrode with low overpotentials at 500 mA cm −2 in both acidic (256 mV) and alkaline electrolytes (292 mV), long-lasting lifetime of over 2400 h (100 d), and high-temperature performance (70 o C) are due to the self-standing hydrophilic porous surface, intrinsic mechanical strength and self-grown MoC (001)–Mo 2 C (101) heterojunctions that have a Δ G H* value of −0.13 eV in acidic condition, and the energy barrier of 1.15 eV for water dissociation in alkaline solution. The preparation of a large electrode (3 cm × 11.5 cm) demonstrates the possibility of scaling up this process to prepare various carbide electrodes with rationally designed structures, tunable compositions, and favorable properties. Scalable fabrication of Low-cost hydrogen evolution reaction (HER) catalysts that can operate at industry-relevant conditions is highly needed for efficient water electrolyzers. Here the authors show a scalable synthesis of a MoC-Mo2C heterojunction electrode with efficient HER activity and high stability at industrial conditions.

Developing highly active and durable electrocatalysts for acidic oxygen evolution reaction remains a great challenge due to the sluggish kinetics of the four-electron transfer reaction and severe catalyst dissolution. Here we report an electrochemical lithium intercalation method to improve both the activity and stability of RuO 2 for acidic oxygen evolution reaction. The lithium intercalates into the lattice interstices of RuO 2 , donates electrons and distorts the local structure. Therefore, the Ru valence state is lowered with formation of stable Li-O-Ru local structure, and the Ru–O covalency is weakened, which suppresses the dissolution of Ru, resulting in greatly enhanced durability. Meanwhile, the inherent lattice strain results in the surface structural distortion of Li x RuO 2 and activates the dangling O atom near the Ru active site as a proton acceptor, which stabilizes the OOH* and dramatically enhances the activity. This work provides an effective strategy to develop highly efficient catalyst towards water splitting. While water splitting in acid offers higher operational performances than in alkaline conditions, there are few high-activity, acid-stable oxygen evolution electrocatalysts. Here, authors examine electrochemical Li intercalation to improve the activity and stability of RuO 2 for acidic water oxidation.

Hydrogen production by electrocatalytic water splitting is an efficient and economical technology, however, is severely impeded by the kinetic-sluggish and low value-added anodic oxygen evolution reaction. Here we report the nickel-molybdenum-nitride nanoplates loaded on carbon fiber cloth (Ni-Mo-N/CFC), for the concurrent electrolytic productions of high-purity hydrogen at the cathode and value-added formate at the anode in low-cost alkaline glycerol solutions. Especially, when equipped with Ni-Mo-N/CFC at both anode and cathode, the established electrolyzer requires as low as 1.36 V of cell voltage to achieve 10 mA cm −2 , which is 260 mV lower than that in alkaline aqueous solution. Moreover, high Faraday efficiencies of 99.7% for H 2 evolution and 95.0% for formate production have been obtained. Based on the excellent electrochemical performances of Ni-Mo-N/CFC, electrolytic H 2 and formate productions from the alkaline glycerol solutions are an energy-efficient and promising technology for the renewable and clean energy supply in the future. Hydrogen production by electrocatalytic water splitting is limited by the sluggish evolution kinetics of low value-oxygen. Here, authors show concurrent electrolytic productions of H 2 and glycerol oxidation to formate by utilizing Ni-Mo-N/CFC electro-catalyst as both anodic and cathodic catalysts.