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Oxygen electrochemistry plays a key role in industrial hydrogen fuel production from water electrolysis, but the slow kinetics of the anodic oxygen evolution reaction (OER) at large current density restricts the commercialization of such energy devices. Here, we design a new class of valence-variable metal-modified CuCo2S4thiospinels, termed as v-M–CuCo2S4/NF (v-M = Mn, V, Cr), to achieve large-current-density OER performance. The introduction of valence-variable metals (v-M) can promote the generation of a special oxyhydroxide-like active phase with a contractive interatomic Co–Co distance, which breaks the limit of the inherent linear scaling relationship and causes the OER on v-M–CuCo2S4/NF to follow a more efficient oxide path mechanism. Therefore, v-M–CuCo2S4/NF, taking Mn–CuCo2S4/NF as a representative, delivers low overpotentials of 255 and 378 mV to achieve large current densities of 500 and 1500 mA cm−2in alkaline electrolytes. The optimal catalyst shows a large mass activity of 3000 A gmetal−1and a high turnover frequency of 16 500 h−1at a low overpotential of 378 mV (1500 mA cm−2), tens of times larger than commercial RuO2/NF. The design principle provides some hints for optimizing abundant spinel materials as large current density OER catalysts.

Proton exchange membrane fuel cell (PEMFC) is a potential candidate as the power source for vehicle application. However, problems related to water and thermal management must be resolved before their large-scale promotion. Numerical models are often used as powerful tools to describe the electrochemical and transport phenomena occurring in PEMFC, which are important to water and thermal management. In this study, two-phase, non-isothermal, transient models are employed to research the local dynamic characteristics inside PEMFC under road driving conditions and different operating conditions. The simulation results indicate that overload running often causes local high temperature, which can lead to membrane dehydration, voltage loss, and power overshoot as load increases. If the temperature is above the glass transition temperature of the membrane, it will even lead to membrane mechanical degradation. According to our research, controlling the operating temperature below 378 K and reducing the coolant temperature in advance are the effective ways to prevent the aforementioned attenuation.

Developing efficient and durable oxygen evolution electrocatalyst is of paramount importance for the large-scale supply of renewable energy sources. Herein, we report a design of significant surface hydrophilicity based on the cobalt oxyhydroxide (CoOOH) nanosheets to greatly improve the surface hydroxyl species adsorption and reaction kinetics at the Helmholtz double layer for high-efficiency water oxidation activity. The as-designed CoOOH-Graphene nanosheets achieve a small surface water contact angle of ~23° and a large double-layer capacitance (Cdl) of 8.44 mF/cm2, thus could evidently strengthen surface species adsorption and trigger electrochemical oxygen evolution reaction (OER) under a quite low onset potential of 200 mV with an excellent Tafel slope of 32 mV/dec. X-ray absorption spectroscopy and first-principles calculations demonstrate that the strong interface electron coupling between CoOOH and graphene extracts partial electrons from the active sties and increases the electron state density around the Fermi level, and effectively promotes the surface intermediates formation for efficient OER.

Highly efficient oxygen evolution driven by abundant sunlight is a key to realize overall water splitting for large-scale conversion of renewable energy. Here, we report a strategy for the interfacial atomic and electronic coupling of layered CoOOH and BiVO4to deactivate the surface trapping states and suppress the charge-carrier recombination for high photoelectrochemical (PEC) water oxidation activity. The successful synthesis of a 3D ultrathin-CoOOH-overlayer-coated coral-like BiVO4photoanode effectively tailors the migration route of photocarriers on the semiconductor/liquid interface to realize a great increase of ∼200% in the photovoltage relative to bare BiVO4, consequently decreasing the corresponding onset potential of PEC water splitting from 0.60 to 0.20 VRHE. As a result, the unique CoOOH/BiVO4photoanode could efficiently perform PEC water oxidation in a neutral aqueous solution (pH = 7) with a high photocurrent density of 4.0 mA/cm2at 1.23 VRHEand a prominent quantum efficiency of 65% at 450 nm. Electronic structural characterizations and theoretical calculations reveal that the combination of layered CoOOH and BiVO4forming interfacial oxo-bridge bonding could greatly eliminate surface trapping states and promote the direct transfer of photogenerated holes from the valence band to the surface water redox potential for water oxidation.

Operando insight into the catalytic kinetics under working conditions is important for further rationalizing the design of advanced catalysts toward efficient renewable energy applications. Here, we enable a ubiquitous carbon material as an efficient acidic oxygen evolution reaction (OER) electrocatalyst, synthesized via a facile and controllable “amino-assisted polymerization and carbonization” strategy. This as-developed metal-free amino-rich hierarchical-network carbon (amino-HNC) framework directly supported on carbon paper can catalyze OER at a quite low overpotential of 281 mV and a small Tafel slope of 96 mV dec–1in an acid solution, and maintain ∼98% of its initial catalytic activity after 100 h oxygen evolution operation. By using the operando synchrotron infrared spectroscopy, a crucial structurally evolved H2N–(*O–C)–C, formed by adsorbing the *O intermediate on the active H2N–C═C moiety, is observed on amino-HNC electrocatalysts during the OER process in the acid medium. Furthermore, theoretical calculations reveal that the optimization of the sp2electronic structure of C═C by amino radicals could effectively lower the kinetic formation barrier of the *O intermediate on the H2N–C═C moiety, contributing to a prominent acidic oxygen-involved catalysis.

Direct water splitting in pure water relying on photocatalysis is an effective way to realize an efficient solar to chemical fuel conversion toward solving the global energy crisis and environmental problems. Here, via a “high-valence metal single-atom confinement” strategy, we effectively modify the valence band structure of the semiconductor photocatalyst toward a spontaneous photocatalytic water splitting in pure water. This as-prepared PtII–C3N4could achieve an efficient photocatalytic water splitting activity with the H2production rate up to ∼140 μmol g–1h–1, about 10 times that of Pt nanoparticle–C3N4(15 μmol g–1h–1). Moreover, the unique PtII–C3N4suspension in pure water exhibits an impressive quantum efficiency of 1.5% at 420 nm under visible light irradiation. Electronic structure characterizations and theoretical calculations reveal that the hybridization of PtII5d and N 2p obviously downward shifts the valence band maximum level of PtII–C3N4by 0.26 V relative to g-C3N4, which could significantly promote the reaction thermodynamics of oxygen evolution toward the high photocatalytic water splitting activity.

The development of organometallic complexes with abundant stable single-atom active sites is highly desirable for cost-effective and commercial electrocatalysis towards renewable energy conversion and storage. Here, we report an atomic-level design and construction of a new type of organometallic Au1Nxsingle-site confined on organic carbon-nitride support as a promising bifunctional electrocatalyst for efficient and durable oxygen reduction (ORR) and evolution reaction (OER) performance. The combination of atomic characterizations and theoretical calculations confirm that the atomically dispersed Au1+atoms are grafted onto carbon-nitride support by covalent Au–N bonds via an amine-induced-reduction strategy, forming atomic Au1Nxsingle-sites with potential oxygen-related catalytic activity. Hence, this developed Au1Nxsingle-site electrocatalyst could exhibit excellent electrocatalytic activity and durability with extraordinarily large mass activities of ~9000 A•gAu−1for ORR at the half-wave potential 0.76 V, and of ~1500 A•gAu−1for OER at overpotential 0.45 V, 20–26 times higher than those of benchmarking Pt/C and RuO2electrocatalysts.

Developing high-performance oxygen evolution reaction (OER) electrocatalysts is of great importance for sustainable and renewable energy conversion and storage. Here, via delocalizing the electron population around the active sites of layered hydrotalcites, we significantly facilitate the electron donation from the active sites in Cr-doped Ni0.75Fe0.25(OH)2.25and greatly reduce the charge transfer barrier by 1 order of magnitude for high OER activity. The Cr-doped Ni0.75Fe0.25(OH)2.25hydrotalcite nanosheets could thus achieve a small overpotential of 235 mV at 10 mA/cm2with an excellent Tafel slope of ∼39 mV/dec. The X-ray absorption fine structure spectroscopy and theoretical calculations reveal that the incorporated Cr ions are substituted for Fe sites in Ni0.75Fe0.25(OH)2.25and the strong overlap of dorbitals between Cr with unpaired delectrons and Fe ions promotes ∼0.3 electron π-donation from Ni2+to neighboring Cr (Fe) ions, and then evidently decreases the adsorption free energy of a water molecule to −1.45 eV for efficient OER performance.

Realizing high-efficiency hydrogen evolution in cost-effective and long-lasting electrocatalysts is critical for global production of clean and sustainable chemical fuels. Here, via modulating the metallic 1T phase in 2H MoS2nanosheets, we greatly improved the conductivity and effective active sites for highly efficient electrocatalytic hydrogen evolution. The as-synthesized 1T-2H MoS2electrocatalyst with a high 1T-phase content of 50% can significantly increase the charge concentration by an order of magnitude and triple the effective active surface sites, successfully boosting the hydrogen evolution reaction (HER) at a quite low overpotential of 126 mV at 10 mA/cm2and a small Tafel slope of 35 mV/dec. Ultraviolet photoelectron spectroscopy and electrochemical characterization reveal that the valence band edges of 1T-2H MoS2are upshifted by 0.15–0.36 eV, which obviously enhances the charge transfer ability of the surface active sites in the basal plane of MoS2for high HER performance.

The dynamic response of proton exchange membrane fuel cells (PEMFCs) to power demand remarkably influences the energy management system (EMS) for hybrid hydrogen vehicle applications. This study established a one-dimensional PEMFC model considering the interfacial gas transport behaviors to investigate the most fundamental dynamic process—step loading. The model provided rigorous analytic equations to describe the transient response of output voltage, and a dimensionless variable, Σ=L/Γgδ/τr=vDvR,was found to link the appearance of undershooting quantitatively with the structural characteristics of components and operating processes. The analytic equations showed that the main reason for undershooting was the weaker capacity of remaining oxygen in the catalyst layer (CL) than the diffusion capacity of gas diffusion media (GDM). Deductions from analytic equations were confirmed by experimental results further and indicated that the degree of undershooting (ΔVOS) was linear to the loading step (ΔI˜), which expressed as ΔVOS=b⋅εΣ4FDc/L−I1⋅ΔIto some extent. The quantitative expressions based on the fundamental theories were achieved in this study and provide new perspectives and methods on the studies of dynamic controlling of the PEMFCs power system.

Producing H2by means of direct photocatalytic water splitting using suspension system is highly desired in efficiently transforming solar energy to chemical energy. Here, using an ultrathin β-CoOOH nanosheet as photocatalyst suspended in aqueous Na2SO3solution, we realize highly efficient and stable photocatalytic hydrogen evolution under visible light irradiation. The as-prepared ultrathin β-CoOOH nanosheets suspension can directly photocatalyze hydrogen evolution in a high rate of 1200 μmol/g/h and large quantum efficiencies of 10.7% at 380 nm, 6.9% at 420 nm, and 2.3% at 450 nm. X-ray photoelectron and X-ray absorption measurements reveal that the excellent hydrogen evolution activity of the β-CoOOH nanosheet is attributed to the surface low-coordinated Co catalytic site, which results in a strong hybridization of Co 3dstates with the S pstates of SO32+, and facilitates the electron transfer to reduce H+. The results may be helpful for designing and understanding two-dimensional oxyhydroxide-based photocatalyst for hydrogen production.

Improving the performance of proton exchange membrane fuel cells (PEMFCs) can help accelerate their large-scale commercial application. In this paper, an agglomerate model is proposed and developed by coupling a one-dimensional local oxygen transport model with a one-dimensional multiphase non-isothermal fuel cell sub-model to study the influences of catalyst dimension parameters (Pt radius, Pt average dispersity, carbon radius) on local oxygen transport and cell performance. And this elaborate model shows that the smaller Pt radius, carbon radius, and the higher Pt average dispersity can reduce the transport distance of oxygen molecules from the pores to the active sites, and then decrease the local resistance. Based on the above understanding, the optimum performance of the optimized cell with a Pt loading of 0.2 mg cm-2is improved by 22%, slightly higher than the original cell with a Pt loading of 0.4 mg cm-2, which achieves a 50% reduction in Pt loading while maintaining the cell performance. This research will give a guide for improving cell performance.