Water electrolysis offers a promising energy conversion and storage technology for mitigating the global energy and environmental crisis, but there still lack highly efficient and pH-universal ...electrocatalysts to boost the sluggish kinetics for both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). Herein, we report uniformly dispersed iridium nanoclusters embedded on nitrogen and sulfur co-doped graphene as an efficient and robust electrocatalyst for both HER and OER at all pH conditions, reaching a current density of 10 mA cm
with only 300, 190 and 220 mV overpotential for overall water splitting in neutral, acidic and alkaline electrolyte, respectively. Based on probing experiments, operando X-ray absorption spectroscopy and theoretical calculations, we attribute the high catalytic activities to the optimum bindings to hydrogen (for HER) and oxygenated intermediate species (for OER) derived from the tunable and favorable electronic state of the iridium sites coordinated with both nitrogen and sulfur.
This study proposes a novel reactive terrain estimation system for humanoid robots from the perspective of a state observer. The design process is as follows: the underfoot force disturbance is ...converted into an underfoot position disturbance by using an admittance system, the disturbance state observation is designed with a closed-loop observation method, and finally, the observation state is switched by using a gait planning-based state machine. This study combines a one-step-ahead prediction technique with the algebraic operation of error dynamics, and the designed observer is called a synchronized error predictive observer. The observation error dynamics are analyzed by using the robustness theory to prove that the proposed method can reduce the ultimate bounded range of the observation error and the error in terrain estimation. This study has been validated through simulation and experiment using the UBTECH-Tsinghua WALKER-1 Prototype, which can accurately estimate the terrain height difference and orientation within 0.02 m-height of ground obstacles. The designed observer can effectively improve the accuracy and further reduce the instability that the gait control system may have to withstand.
The solubilities of fluorene in Exxsol D30, Exxsol D40, and crude dimethyl ethylbenzene (DME) from 299.25 to 356.85 K were investigated using the gas chromatography (GC) observation technique. ...Solubility curves were obtained based on the results and correlated with the modified Apelblat and
λh
equations to provide a valid model to predict the dissolution thermodynamic properties of fluorene at different temperatures, which is important in separating fluorene by crystallization.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This article presents a model-based control method for achieving bipedal locomotion of a position-controlled humanoid robot on uneven terrain. The method is called model reference one-step-ahead ...predictive control (MROPC), which considers the tracking error of the next cycle in each control period to improve system responsiveness. To achieve this, it utilizes an inverted pendulum model and a whole-body kinematic model, both of which are set on an equivalent slope, using inertial measurement unit (IMU), encoders, and foot sensors to estimate the local slope of the ground. Through Lyapunov stability analysis, it is proven that MROPC is more robust than the well-known virtual spring damping (VSD) and proportional-derivative (PD) control, effectively suppressing disturbance energy and improving robustness. To verify the theoretical results, tests were first conducted in a simulation environment, and frequency response analysis using Bode plot showed that MROPC performed better at frequencies up to 2 Hz. Then, to check real-world capabilities, the algorithm was deployed on the WALKER-I and tested in several disturbance scenarios such as the unstable plank with a rod placed halfway under it, and applications with active terrain estimation, such as sudden placement of small steps on flat ground under the feet. Ultimately, it achieves an anti-disturbance function on uneven terrain.
The electrochemical hydrogen evolution reaction (HER) that converts renewable electricity into storable hydrogen, a sustainable and clean energy carrier, provides a promising method to mitigate the ...energy crisis and environmental pollution. In general, noble‐metal‐based nanomaterials (including Pt, Rh, Ru, Ir, etc.) have drawn tremendous research attention in the context of the HER because of their nearly optimal bindings to hydrogen, robust stability and tunable physical/chemical properties. Particularly, carbon as a substrate not only offers a stabilizing and conductive matrix, but also impacts the electronic structure of the supported metal by interfacial interaction, necessitating a detailed understanding. To speed up the sluggish kinetics of the HER, the design and construction of efficient electrocatalysts is of crucial importance. Herein, a comprehensive review of the recent advances in carbon‐supported noble‐metal electrocatalysts is presented, focusing on their synthetic strategies, structural analyses, and applications in HER electrocatalysis. Specifically, the correlation between the electronic structure and activity is discussed. Furthermore, a perspective is offered highlighting the challenges and opportunities for development of highly efficient HER electrocatalysts, with the aim for widespread utilization of practical water electrolyzers toward green hydrogen production.
The pros and cons of the strategies to construct carbon‐based noble metal hydrogen evolution reaction catalysts including loading noble metals on carbon substrates and carbonizing noble metal/carbon precursor mixtures are analyzed. Subsequently, the methods to optimize the hydrogen adsorption energy and proton transport via structure engineering are summarized. Finally, the challenges for practical water electrolysis are discussed.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Designing and synthesizing highly efficient and stable electrocatalysts for hydrogen evolution reaction (HER) is important for realizing the hydrogen economy. Tuning the electronic structure of the ...electrocatalysts is essential to achieve optimal HER activity, and interfacial engineering is an effective strategy to induce electron transfer in a heterostructure interface to optimize HER kinetics. In this study, ultrafine RhP2/Rh nanoparticles are synthesized with a well‐defined semiconductor–metal heterointerface embedded in N,P co‐doped graphene (RhP2/Rh@NPG) via a one‐step pyrolysis. RhP2/Rh@NPG exhibits outstanding HER performances under all pH conditions. Electrochemical characterization and first principles density functional theory calculations reveal that the RhP2/Rh heterointerface induces electron transfer from metallic Rh to semiconductive RhP2, which increases the electron density on the Rh atoms in RhP2 and weakens the hydrogen adsorption on RhP2, thereby accelerating the HER kinetics. Moreover, the interfacial electron transfer activates the dual‐site synergistic effect of Rh and P of RhP2 in neutral and alkaline environments, thereby promoting reorganization of interfacial water molecules for faster HER kinetics.
The RhP2/Rh heterointerface induces electron transfer from metallic Rh to semiconductive RhP2, which effectively increases the electron density on the Rh atoms in RhP2 and weakens the hydrogen adsorption on RhP2. The interfacial electron transfer can activate the dual‐site synergistic effect of Rh and P of RhP2, effectively promoting reorganization of interfacial water molecules for faster hydrogen evolution reaction (HER) kinetics.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A molecular simulation is developed to study the effect of surface nanostructures on nanoscale flows. Based on this method, particles equation of motion is solved through the Verlet algorithm. ...Meanwhile, a physically sound method is applied to control the momentum and temperature of the simulation box. By adding an external force on the top copper plate according to the velocity difference between on-the-fly and desired velocities, simulations on convection of argon flows between two solid walls are performed. The top wall, which holds a higher temperature, moves at a constant velocity relative to bottom one along with the streamwise direction. These simulation results show that the nanostructures particularly affect fluid density oscillations adjacent to solid wall and nanostructures. In addition, these nanostructures also have significant effects on temperature and velocity distributions in simulation system.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Polymer electrolyte membrane water electrolysis (PEMWE) has been regarded as a promising technology for renewable hydrogen production. However, acidic oxygen evolution reaction (OER) catalysts with ...long‐term stability impose a grand challenge in its large‐scale industrialization. In this review, critical factors that may lead to catalyst's instability in couple with potential solutions are comprehensively discussed, including mechanical peeling, substrate corrosion, active‐site over‐oxidation/dissolution, reconstruction, oxide crystal structure collapse through the lattice oxygen‐participated reaction pathway, etc. Last but not least, personal prospects are provided in terms of rigorous stability evaluation criteria, in situ/operando characterizations, economic feasibility and practical electrolyzer consideration, highlighting the ternary relationship of structure evolution, industrial‐relevant activity and stability to serve as a roadmap towards the ultimate application of PEMWE.
The large‐scale application of polymer electrolyte membrane water electrolysis (PEMWE) is suffering from long‐term stability challenges in anodic oxygen evolution reaction (OER). This review provides a thorough discussion of degradation mechanisms, catalyst design principles and future research opportunities to serve as a cornerstone for overcoming the dilemma in acidic OER stability and achieving the industrialization of water electrolysis.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Developing highly active and stable water oxidation catalysts with reduced cost in acidic media plays a critical role in clean energy technologies such as fuel cells and electrolyzers. Precious ...iridium-based oxides are still the only oxygen evolution reaction (OER) catalysts with reasonable activity and stability in acid. Herein, we design iridium-tungsten composites with a metallic tungsten-rich core and an iridium-rich surface by the sol-gel method followed by hydrogen reduction. The thus obtained iridium-tungsten catalyst shows much higher intrinsic water oxidation activity (100 mA/mg
at an overpotential of 290 mV) and stability (100 h at 10 mA/cm
) together with reduced iridium content (33 wt % only) as compared with pure iridium oxide. An operando method using H
O
as a probe molecule is developed to determine the relative adsorption strength of the reaction intermediates (*OH and *OOH) in the OER process. Detailed characterization shows that the tungsten-incorporated surface not only modulates the adsorption energy of oxygen intermediates on iridium but also enhances the stability of iridium species in acid, while the metallic tungsten core exhibits high electrical conductivity, all of which collectively give rise to the much enhanced catalytic performance of iridium-tungsten composite in acidic water oxidation. A single-membrane electrode assembly is further prepared to demonstrate the advantages and potential application of iridium-tungsten composite in practical proton exchange membrane electrolyzers.
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IJS, KILJ, NUK, PNG, UL, UM
The design of active and low-cost electrocatalyst for hydrogen evolution reaction (HER) is the key to achieving a clean hydrogen energy infrastructure. The most successful design principle of ...hydrogen electrocatalyst is the activity volcano plot, which is based on Sabatier principle and has been used to understand the exceptional activity of noble metal and design of metal alloy catalysts. However, this application of volcano plot in designing single-atom electrocatalysts (SAEs) on nitrogen doped graphene (TM/N4C catalysts) for HER has been less successful due to the nonmetallic nature of the single metal atom site. Herein, by performing ab initio molecular dynamics simulations and free energy calculations on a series of SAEs systems (TM/N4C with TM = 3d, 4d, or 5d metals), we find that the strong charge–dipole interaction between the negatively charged *H intermediate and the interfacial H2O molecules could alter the transition path of the acidic Volmer reaction and dramatically raise its kinetic barrier, despite its favorable adsorption free energy. Such kinetic hindrance is also experimentally confirmed by electrochemical measurements. By combining the hydrogen adsorption free energy and the physics of competing interfacial interactions, we propose a unifying design principle for engineering the SAEs used for hydrogen energy conversion, which incorporates both thermodynamic and kinetic considerations and allows going beyond the activity volcano model.
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IJS, KILJ, NUK, PNG, UL, UM
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