mA Cm-2 Current Density Research Articles

Evolution of Mn-Bi2O3 from the Mn-doped Bi3O4Br electro(pre)catalyst during the oxygen evolution reaction.

Mn-doped Bi3O4Br has been synthesized using a solvothermal route. The undoped Bi3O4Br and Mn-Bi3O4Br materials possess orthorhombic unit cells with two distinct Bi sites forming a layered atomic arrangement. The shift in the (020) plane in the powder X-ray diffraction (PXRD) pattern confirms Mn-doping in the Bi3O4Br lattice. Elemental mapping indicated 7% Mn doping in the Bi3O4Br lattice structure. A core-level X-ray photoelectron study (XPS) indicates the presence of BiIII and MnII valence-states in Mn-Bi3O4Br. Doping with a cation (MnII) containing a different charge and ionic radius resulted in vacancy/defects in Mn-Bi3O4Br which further altered its electronic structure by reducing the indirect band gap, beneficial for electron conduction and electrocatalysis. The irreversible MnII to MnIII transformation at a potential of 1.48 V (vs. RHE) precedes the electrochemical oxygen evolution reaction (OER). The Mn-doped electrocatalyst achieved 10 mA cm-2 current density at 337 mV overpotential, while the pristine Bi3O4Br required 385 mV overpotential to reach the same activity. The pronounced OER activity of the Mn-Bi3O4Br sample over the pristine Bi3O4Br highlights the necessity of MnII doping. The superior activity of the Mn-Bi3O4Br catalyst over that of Bi3O4Br is due to a low Tafel slope, better double-layer capacitance (Cdl), and small charge-transfer resistance (Rct). The chronoamperometry (CA) study depicts long-term stability for 12 h at 20 mA cm-2. An electrolyzer fabricated as Pt(-)/(+)Mn-Bi3O4Br can deliver 10 mA cm-2 at a cell potential of 2.05 V. The post-CA-OER analyses of the anode confirmed the leaching of [Br-] followed by in situ formation of Mn-doped Bi2O3 as the electrocatalytically active species. Herein, an ultra-low Mn-doping into Bi3O4Br leads to an improvement in the electrocatalytic performance of the inactive Bi3O4Br material.

Ruthenium-doped cobalt sulphide electrocatalyst derived from a ruthenium-cobalt Prussian blue analogue (RuCo-PBA) for an enhanced hydrogen evolution reaction (HER).

The designing of efficient electrocatalysts for hydrogen generation is essential for the practical application of water-splitting devices. With numerous electrochemical advantages, transition metal sulphides are regarded as the most promising candidates for catalysing the hydrogen evolution reaction (HER) in acidic media. In the present study, Ru-doped cobalt sulphide nanosheets, termed Co9S8/Ru@t (t = 24 h, 48 h, and 72 h), were obtained by varying the reaction time from 24 h to 72 h from a RuCo-PBA precursor. The role of the time period for the synthesis of Co9S8/Ru@48h is vital in increasing the number of electroactive sites and optimising the hydrogen adsorption-desorption phenomena leading to an increment in the HER activity. The electrochemical outcomes demonstrate that the optimized Co9S8/Ru@48h requires a low overpotential of just 94 mV to produce 10 mA cm-2 current density, and also exhibits a lower Tafel slope value of 84 mV dec-1 defining its faster reaction kinetics. The as-synthesized Co9S8/Ru@48h was stable for up to 20 h of constant electrolysis signifying its outstanding durability. The optimized synthetic approach and impressive electrochemical results make Co9S8/Ru@48h a suitable alternative to noble-metal-based electrocatalysts for the HER.

Insights of the efficient hydrogen evolution reaction performance in bimetallic Au4Cu2 nanoclusters.

The design of efficient electrocatalysts for improving hydrogen evolution reaction (HER) performance using atomically precise metal nanoclusters (NCs) is an emerging area of research. Here, we have studied the HER electrocatalytic performance of monometallic Cu6 and Au6 nanoclusters and bimetallic Au4Cu2 nanoclusters. A bimetallic Au4Cu2/MoS2 composite exhibits excellent HER catalytic activity with an overpotential (η10) of 155 mV vs. reversible hydrogen electrode observed at 10 mA cm-2 current density. The improved HER performance in Au4Cu2 is due to the increased electrochemically active surface area (ECSA), and Au4Cu2 NCs exhibits better stability than Cu6 and Au6 systems and bare MoS2. This augmentation offers a greater number of active sites for the favorable adsorption of reaction intermediates. Furthermore, by employing X-ray photoelectron spectroscopy (XPS) and Raman analysis, the kinetics of HER in the Au4Cu2/MoS2 composite were elucidated, attributing the favorable performance to better electronic interactions occurring at the interface between Au4Cu2 NCs and the MoS2 substrate. Theoretical analysis reveals that the inherent catalytic enhancement in Au4Cu2/MoS2 is due to favorable H atom adsorption over it and the smallest ΔGH* value. The downshift in the d-band of the Au4Cu2/MoS2 composite influences the binding energy of intermediate catalytic species. This new catalyst sheds light on the structure-property relationship for improving electrocatalytic performance at the atomic level.

Iron-impregnated cellulosic carbon as an effective electrocatalyst for seawater oxidation.

The quest for cost effective but active electrocatalysts for water oxidation is at the forefront of research towards hydrogen economy. In this regard, bamboo as biomass derived N-doped cellulosic carbon has shown potential electrocatalytic performance towards water oxidation. The impregnation of optimum metallic Fe boosts the performance further, achieving an overpotential value of 238 mV at a benchmark current density of 10 mA cm-2. Owing to its promising OER performances in alkaline freshwater, the electrocatalyst was further explored in alkaline saline water and alkaline real seawater, exhibiting overpotentials of 272 mV and 280 mV, respectively, to reach 10 mA cm-2 current density. Most importantly, the protective graphitic multilayer surrounding the metallic Fe allowed the electrocatalyst to demonstrate excellent durability over 30 h even at a high current density in alkaline real seawater electrolyte.

Layered MOF supported on 2D delaminated MXene (Mo2Ti2C3) nanosheets boosted water splitting.

Metal organic frameworks (MOFs) have a porous structure, high surface area, and high charge transfer, and they have been regarded as model electrocatalysts. Optimization of the electrocatalytic activity of MOFs is challenging, and an effective strategy for this optimization is the construction of a well-defined interfacial bond bridge. In this work, an in situ approach of composite synthesis is reported for MOF (CoNiNH2BDC) with MXenes (Mo2Ti2C3), as the electrocatalytic properties of MOF can be greatly enhanced with the incorporation of the conductive material MXene. The prepared composite material was characterized thoroughly using XRD, XPS, FESEM, EDX, TEM, and BET. The synergistic effect of both components of this composite material resulted in enhanced conductivity and the number of active sites, which led to enhanced electrocatalytic performance. The CoNiNH2BDC MOF with different ratios of Mo2Ti2C3 MXene were synthesized, and the resulting materials were evaluated for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities. It was observed that the MOFMX3 attained a 10 mA cm-2 current density at 1.44 V for OER and -0.037 V for HER (vs. RHE), and lower values of Tafel slopes of 44.8 mV dec-1 for OER and 45 mV dec-1 for HER in 0.1 M KOH were achieved. The higher double layer capacitance (C dl) values lead to high electrochemical surface area (ECSA) values. Lower Tafel slope values for MOFMX3 show that the presence of MXene nanosheets in the hybrid provides support to the layered and porous configuration of MOF, and the chances of the interaction of electrolyte to the catalytically active sites are significantly enhanced. This work highlights the idea of growing bimetallic MOFs on Mo2Ti2C3 MXene using an interdiffusion reaction strategy and opens up an avenue for designing highly electrocatalytic systems.

Reinforcement of Electrocatalytic Oxygen Evolution Activity Enabled by Constructing Silver-Incorporated NiCo-PBA@NiFe-LDH Hierarchical Nanoboxes.

Complicated oxygen evolution reaction (OER) poses the bottleneck in improving the efficiency of hydrogen production through water electrolysis. Herein, an integrated strategy to modulate the electronic structure of NiFe layered double hydroxide (NiFe-LDH) is reported by constructing Ag-incorporated NiCo-PBA@NiFe-LDH heterojunction with a hierarchical hollow structure. This "double heterojunction" facilitates local charge polarization at the interface, thereby promoting electron transfer and reducing the adsorption energy of intermediates, ultimately enhancing the intrinsic activity of the catalyst. It is noteworthy that an exchange bias field is observed between NiCo-PBA and NiFe-LDH, which will be conducive to regulating the electron spin states of metals and facilitating the production of triplet oxygen. Additionally, the unique hierarchical nanoboxes provide a large specific surface area that ensures adequate exposure to adsorption sites and active sites. Profiting from the synergistic advantages, the overpotential is as low as 190mV at a current density of 10mAcm-2, with a low Tafel slope of 21mVdec-1. Moreover, density functional theory (DFT) calculation further substantiated that the incorporation of Ag in the heterojunction can effectively reduce the adsorption energy of reactant intermediates and enhance the conductivity.

Biomineralization of Sulfate-Reducing Bacteria In Situ-Induced Preparation of Nano Fe2O3-Fe(Ni)S/C as High-Efficiency Oxygen Evolution Electrocatalyst.

Transition metal-based catalysts possess high catalytic activity for oxygen evolution reaction (OER). However, the preparation of high-performance OER electrocatalysts using simple strategies with a low cost still faces a major challenge. Herein, this work presents an innovative, in situ-induced preparation of the Fe2O3, FeS, and NiS nanoparticles, supported on carbon blacks (CBs) (denoted as Fe2O3-Fe(Ni)S/C) as a high-efficiency oxygen evolution electrocatalyst by employing biomineralization. Biomineralization, a simple synthesis strategy, demonstrates a huge advantage in controlling the size of the Fe2O3 and Fe(Ni)S nanoparticles, as well as achieving uniform nanoparticle distribution on carbon blacks. It is found that the electrocatalyst Fe2O3-Fe(Ni)S/C-200 shows a good OER electrocatalytic activity with a small loading capacity, and it has a small overpotential and Tafel slope in 1 m KOH solution with values of 264mV and 42mVdec-1, respectively, at a current density of 10mAcm-2. Additionally, it presents good electrochemical stability for over 24h. The remarkable and robust electrocatalytic performance of Fe2O3-Fe(Ni)S/C-200 is attributed to the synergistic effect of Fe2O3, FeS, and doped-Ni species as well as its distinct 3D spherical structure. This approach indicates the promising applications of biomineralization for the bio-preparation of functional materials and energy conversion.

A Conductive 3D Dual-Metal π-d Conjugated Metal-Organic Framework Fe3(HITP)2/bpm@Co for Highly Efficient Oxygen Evolution Reaction.

Although 2Dπ-d conjugated metal-organic frameworks (MOFs) exhibit high in-plane conductivity, the closely stacked layers result in low specific surface area and difficulty in mass transfer and diffusion. Hence, a conductive 3DMOF Fe3(HITP)2/bpm@Co (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) is reported through inserting bpm (4,4'-bipyrimidine) ligands and Co2+ into the interlayers of 2D MOF Fe3(HITP)2. Compared to 2D Fe3(HITP)2 (37.23m2g-1), 3D Fe3(HITP)2/bpm@Co displays a huge improvement in the specific surface area (373.82m2g-1). Furthermore, the combined experimental and density functional theory (DFT) theoretical calculations demonstrate the metallic behavior of Fe3(HITP)2/bpm@Co, which will benefit to the electrocatalytic activity of it. Impressively, Fe3(HITP)2/bpm@Co exhibits prominent and stable oxygen evolution reaction (OER) performance (an overpotential of 299mV vs RHE at a current density of 10mAcm-2 and a Tafel slope of 37.14mVdec-1), which is superior to 2D Fe3(HITP)2 and comparable to commercial IrO2. DFT theoretical calculation reveals that the combined action of the Fe and Co sites in Fe3(HITP)2/bpm@Co is responsible for the enhanced electrocatalytic activity. This work provides an alternative approach to develop conductive 3D MOFs as efficient electrocatalysts.

Selective Shielding of the (002) Plane Enabling Vertically Oriented Zinc Plating for Dendrite-Free Zinc Anode.

Uncontrolled growth of Zn dendrites hinders the future development of aqueous Zn-ion batteries. Despite that the (100) plane possesses better zincophilic ability and fast kinetics, dendrites are generally suppressed via (002) plane-oriented Zn deposition in previous reports; the ordered (100) plane-dominant Zn deposition, especially under high current density has not yet been realized. Herein, vertically-oriented Zn plating with preferential growth of (100) plane is reported using disodium lauryl phosphate (DLP) as an electrolyte additive. DLP is preferentially anchored on the Zn (002) crystal plane via the polar phosphate group, then the deposition of Zn atoms on the (002) plane is retarded by the long alkyl chain, finally promoting the preferred growth of the (100) plane. This unique growth pattern results in ultrastable Zn plating/stripping at a super-high current density of 50mA cm-2 , with a cumulative capacity of 8500 mAh cm-2 . The Zn//Zn symmetric cell also cycles steadily for 700h with a large areal capacity of 10 mAh cm-2 at a current density of 10mA cm-2 . This study provides new insights into the realization of dendrite-free Zn anodes by crystal plane modulation.

Heterostructured Bimetallic MOF-on-MOF Architectures for Efficient Oxygen Evolution Reaction.

Electron modulation presents a captivating approach to fabricate efficient electrocatalysts for the oxygen evolution reaction (OER), yet it remains a challenging undertaking. In this study, an effective strategy is proposed to regulate the electronic structure of metal-organic frameworks (MOFs) by the construction of MOF-on-MOF heterogeneous architectures. As a representative heterogeneous architectures, MOF-74 on MOF-274 hybrids are in situ prepared on 3D metal substrates (NiFe alloy foam (NFF)) via a two-step self-assembly method, resulting in MOF-(74 + 274)@NFF. Through a combination of spectroscopic and theory calculation, the successful modulation of the electronic property of MOF-(74 + 274)@NFF is unveiled. This modulation arises from the phase conjugation of the two MOFs and the synergistic effect of the multimetallic centers (Ni and Fe). Consequently, MOF-(74 + 274)@NFF exhibits excellent OER activity, displaying ultralow overpotentials of 198 and 223mV at a current density of 10mA cm-2 in the 1.0 and 0.1M KOH solutions, respectively. This work paves the way for manipulating the electronic structure of electrocatalysts to enhance their catalytic activity.

Regulation of Sulfur Atoms in MoSx by Magneto-Electrodeposition for Hydrogen Evolution Reaction.

Compared with crystalline molybdenum sulfide (MoS2) employed as an efficient hydrogen evolution reaction (HER) catalyst, amorphous MoSx exhibits better activity. To synthesize amorphous MoSx, electrodeposition serving as a convenient and time-saving method is successfully applied. However, the loading mass is hindered by limited mass transfer efficiency and the available active sites require further improvement. Herein, magneto-electrodeposition is developed to synthesize MoSx with magnetic fields up to 9 T to investigate the effects of a magnetic field in the electrodeposition processing, as well as the induced electrochemical performance. Owing to the magneto-hydrodynamic effect, the loading mass of MoSx is obviously increased, and the terminal S2- serving as the active site is enhanced. The optimized MoSx catalyst delivers outstanding HER performance, achieving an overpotential of 50mV at a current density of 10mA cm-2 and the corresponding Tafel slope of 59mV dec-1. The introduction of a magnetic field during the electrodeposition process will provide a novel route to prepare amorphous MoSx with improved electrochemical performance.

Modulating Electronic Structure and Atomic Insights into the Novel Hierarchically Porous PdCuFe Trimetallic Alloy Aerogel for Efficient Oxygen Reduction.

The high cost of noble Pd/Pt required for the oxygen reduction reaction (ORR) in the cathode restricts the wide applications of fuel cells. In this study, the synthesis of a novel Pd3CuFe0.5 aerogel electrocatalyst is successfully demonstrated using self-assembly and lyophilization techniques, employing a mild reducing agent. The resulting aerogel electrocatalyst exhibits a distinctive 3D network structure, possessing a substantial BET-specific surface area of 75.19 m2g-1. It is worth noting that the optimized Pd3CuFe0.5 aerogel demonstrates exceptional ORR performance with a high half-wave potential of 0.92V versus RHE, a significant limiting current density of 7.6mAcm-2, and the excellent electrocatalytic stability, superior to the reported noble metal electrocatalysts, with the ORR activity decays only 4.9% after 16000 s. In addition, the Pd3CuFe0.5 aerogel electrocatalyst shows superior cycling stability for ≈120h at a charge/discharge current density of 10mAcm-2, indicating its promising application in fuel cells. Furthermore, the resulting composite aerogel possesses excellent hydrogen evolution reaction and ethanol oxidation reaction activity. The density functional theory calculations show that the partial oxidation of Pd3CuFe0.5 aerogel leads to a negative shift of the d-band center, which energetically optimizes the binding strength of *O intermediates, therefore accelerating the ORR activity.

Low-Cost Hydrogen Production from Alkaline/Seawater over a Single-Step Synthesis of Mo3 Se4 -NiSe Core-Shell Nanowire Arrays.

The rational design and steering of earth-abundant, efficient, and stable electrocatalysts for hydrogen generation is highly desirable but challenging with catalysts free of platinum group metals (PGMs). Mass production of high-purity hydrogen fuel from seawater electrolysis presents a transformative technology for sustainable alternatives. Here, a heterostructure of molybdenum selenide-nickel selenide (Mo3 Se4 -NiSe) core-shell nanowire arrays constructed on nickel foam by a single-step in situ hydrothermal process is reported. This tiered structure provides improved intrinsic activity and high electrical conductivity for efficient charge transfer and endows excellent hydrogen evolution reaction (HER) activity in alkaline and natural seawater conditions. The Mo3 Se4 -NiSe freestanding electrodes require small overpotentials of 84.4 and 166mV to reach a current density of 10mA cm-2 in alkaline and natural seawater electrolytes, respectively. It maintains an impressive balance between electrocatalytic activity and stability. Experimental and theoretical calculations reveal that the Mo3 Se4 -NiSe interface provides abundant active sites for the HER process, which modulate the binding energies of adsorbed species and decrease the energetic barrier, providing a new route to design state-of-the-art, PGM-free catalysts for hydrogen production from alkaline and seawater electrolysis.

Polymer Coating with Balanced Coordination Strength and Ion Conductivity for Dendrite-Free Zinc Anode.

Decorating Zn anodes with functionalized polymers is considered as an effective strategy to inhibit dendrite growth. However, this normally brings extra interfacial resistance rendering slow reaction kinetics of Zn2+ . Herein, a poly(2-vinylpyridine) (P2VP) coating with modulated coordination strength and ion conductivity for dendrite-free Zn anode is reported. The P2VP coating favors a high electrolyte wettability and rapid Zn2+ migration speed (Zn2+ transfer number, tZn 2+ = 0.58). Electrostatic potential calculation shows that P2VP mildly coordinates with Zn2+ (adsorption energy = -0.94eV), which promotes a preferential deposition of Zn along the (002) crystal plane. Notably, the use of partially (26%) quaternized P2VP (q-P2VP) further reduces the interfacial resistance to 126 Ω, leading to a high ion migration speed (tZn 2+ = 0.78) and a considerably low nucleation overpotential (18mV). As a result of the synergistic effect of mild coordination and partial electrolysis, the overpotential of the q-P2VP-decorated Zn anode retains at a considerably low level (≈46mV) over 1000h at a high current density of 10mA cm-2 . The assembled (NH4 )2 V6 O16 ·1.5H2 O || glass fiber || q-P2VP-Zn full cell reveals a lower average capacity decay rate of only 0.018% per cycle within 500 cycles at 1 A g-1 .

Fe Cluster Modified Co9 S8 Heterojunction: Highly Efficient Photoelectrocatalyst for Overall Water Splitting and Flexible Zinc-Air Batteries.

Designing bifunctional low-cost photo-assisted electrocatalysts for converting solar and electric energy into hydrogen energy remains a huge challenge. Herein, a heterojunction (Fe cluster modified Co9 S8 loaded on carbon nanotubes, Co9 S8 -Fe@CNT)for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is demonstrated. Benefiting from the good electronic conductivity and spatial confinement of the carbon skeleton, as well as the electronic structure regulation of the Fe cluster, Co9 S8 -Fe@CNT exhibits excellent catalytic performance with a low overpotential of 150mV for OER and 135mV for HER at 10mAcm-2 . Upon light irradiation, holes and electrons are generated in the valence band and conduction band of the Co9 S8 , respectively. Part of the charges are transferred to the interface to facilitate the catalytic reaction, while the remaining are transferred by the electrode. When working as a bifunctional catalyst for overall water splitting, the performance can reach 1.33V at under light conditions, which is significantly better than 1.52V in a dark environment. Theoretical calculations revealed lowered Gibbs free energy (∆GH *) of the heterojunction with the effect of Fe modification of Co9 S8 . This work sheds a new light in designing novel photoelectrochemical materials to convert solar and electric energy into chemical energy.

Heterostructured MoO3 Anchored Defect-Rich NiFe-LDH/NF as a Robust Self-Supporting Electrocatalyst for Overall Water Splitting.

The rational design of inexpensive metal electrocatalysts with exciting catalytic activity for overall water splitting (OWS) remains a significant challenge. Heterostructures of NiFe layered double hydroxides (NiFe-LDHs) with abundant oxygen defects and tunable electronic properties have garnered considerable attention. Here, a self-supporting heterostructured catalyst (named MoO3/NiFe-NF) is synthesized via a hydrothermal method to grow NiFe-LDH with oxygen vacancies (OV) in situ on inexpensive nickel foam (NF). Subsequently, MoO3 is anchored and grown on the surface of NiFe-LDH by electrodeposition. The obtained catalysts achieved outstanding oxygen/hydrogen evolution reaction (OER/HER, 212mV/85mV@10mAcm-2) performance in 1mKOH. Additionally, when MoO3/NiFe-NF is utilized as the cathode and anode in OWS, a current density of 10mAcm-2 can be obtained as an ultralow battery voltage of 1.43V, a significantly lower value compared to the commercial electrolyzer incorporating Pt/C and IrO2 electrode materials. Finally, density functional theory (DFT) calculations and advanced spectroscopy technology are conducted to reveal the effects of heterojunctions and OV on the internal electronic structure of the electrical catalysts. Mainly, the present study provides a novel tactic for the rational design of remarkable, low-cost NiFe-LDH electrocatalysts with heterostructures for OWS.

Magnetic field assisted synthesis of dense braided rope NiCoP as a highly efficient hydrogen evolution electrocatalyst

The design of efficient stable and noble metal-free catalysts for the hydrogen evolution reaction is an important and challenging global task. In this work, high catalytic activity NiCoP braided rope was prepared by magneto-electrodeposition strategy for the first time. Notably, the magnetic field-induced magnetohydrodynamic effect serves multiple purposes. COMSOL numerical simulations reveal the formation mechanism of a braided rope structure. Density functional theory (DFT) calculations confirm that NiCoP has superior activity, attributed to Co active sites. In 1.0 M KOH and 0.5 M H2SO4, respectively, the overpotential of NiCoP prepared under 600 mT magnetic field (NiCoP-600) is only 48 and 34 mV at a current density of 10 mA cm−2. Additionally, the TOF of NiCoP-600 was 36 times as high as that of NiCoP at an overpotential of 100 mV. Furthermore, NiCoP-600 can be used as the cathode and anode for overall water splitting in an alkaline electrolyzer.

Atomic Zincophilic Sites Regulating Microspace Electric Fields for Dendrite-Free Zinc Anode.

Aqueous Zn metal batteries are promising candidates for large-scale energy storage due to their intrinsic advantages. However, Zn tends to deposit irregularly and forms dendrites driven by the uneven space electric field distribution near the Zn-electrolyte interphase. Herein it is demonstrated that trace addition of Co single atom anchored carbon (denoted as CoSA/C) in the electrolyte regulates the microspace electric field at the Zn-electrolyte interphase and unifies Zn deposition. Through preferential adsorption of CoSA/C on the Zn surface, the atomically dispersed Co-N3 with strong charge polarization effect can redistribute the local space electric field and regulate ion flux. Moreover, the dynamic adsorption/desorption of CoSA/C upon plating/stripping offers sustainable long-term regulation. Therefore, Zn||Zn symmetric cells with CoSA/C electrolyte additive deliver stable cycling up to 1600h (corresponding to a cumulative plated capacity of 8 Ah cm-2 ) at a high current density of 10mA cm-2 , demonstrating the sustainable feature of microspace electric field regulation at high current density and capacity.

Nitrided Rhodium Nanoclusters with Optimized Water Bonding and Splitting Effects for pH-Universal H2-Production.

The nitridation of noble metals-based catalysts to further enhance their hydrogen evolution reaction (HER) kinetics in neutral and alkaline conditions would be an effective strategy for developing high-performance wide pH HER catalysts. Herein, a facile molten urea method is employed to construct the nitrided Rh nanoclusters (RhxN) supported on N-doped carbon (RhxN-NC). The uniformly distributed RhxN clusters exhibited optimized water bonding and splitting effects, therefore resulting in excellent pH-universal HER performance. The optimized RhxN-NC catalyst only requires 8, 12, and 109mV overpotentials to reach the current density of 10mA cm-2 in 0.5M H2SO4, 1.0M KOH, and 1.0M PBS electrolytes, respectively. The spectroscopic characterizations and theoretical calculation further confirm the vital role of Rh-N moieties in RhxN clusters in improving the transfer of electrons and facilitating the generation of H2. This work not only provides a suitable nitridation method for noble metal species in mild conditions but also makes a breakthrough in synthesizing noble metal nitrides-based electrocatalysts to achieve an exceptional wide-pH HER performance and other catalysis.

Graphene-Doped Hydrogels Promoting Ionic Conductivity in Gel-Valve-Regulated Lead Acid Batteries.

In this study, the impact of graphene-doped poly(vinyl alcohol) hydrogels on gel-valve-regulated lead acid batteries was examined. The gel formulations were made by adding various amounts of graphene into the gel system comprising poly(vinyl alcohol) and sulfuric acid. Gel formulations were subjected to an ionic conductivity study and Fourier transform infrared spectroscopy (FTIR) to understand ionic mobility and material interaction, respectively. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) were utilized to find the optimized amount of graphene in gel formulations. Galvanostatic charge-discharge (GCD) techniques were employed on a battery comprising an optimized gel electrolyte. The battery exhibited a discharge capacity of 12.82 mAh at a current density of 15 mA cm-2. After 500 prolonged cycles, the battery displayed a discharge capacity of 87% at 25 mA cm-2 current density, indicating that graphene-doped hydrogels can be a promising gel electrolyte for lead acid batteries.