Alkaline HER Research Articles

Ru Nanoparticles on Carbon Skeletons for an Efficient Hydrogen Evolution Reaction in Alkaline Electrolyte

AbstractThe search of alkaline HER electrocatalysts with high performance have attracted great research attentions in recent years. For the construction of the electrocatalysts, a stable conductive substrate is generally required to the uniform distribution of the catalytic materials, where carbon‐based materials are widely utilized. Herein, porous carbon skeletons were prepared after the annealing treatment of Al‐porous coordination polymers with high specific surface area as the substrates for the growth of Ru nanoparticles via wet chemical reduction. The obtained electrocatalysts show a low overpotential of 39 mV at a current density of 10 mA cm−2 and a small Tafel slope of 26 mV dec−1 in 1 M KOH, outperforming the commercial Pt/C. The present work may provide new insights for the design of economy and high‐efficiency electrocatalysts for hydrogen production.

Nickel sulfide-oxide heterostructured electrocatalysts: Bi-functionality for overall water splitting and in-situ reconstruction

Bi-functional electrocatalysts are desired for both hydrogen and oxygen evolution reactions (HER and OER). Herein, facile O2-plasma activation is introduced to improve the bi-functionality via constructing nickel sulfide-oxide heterostructures. Ni3S2-NiOx supported by nickel foam delivers obviously elevated HER and OER activity in comparison with pristine Ni3S2 and recently reported NiSx-based electrocatalysts, featured by the low overpotentials for HER (104 mV) and OER (241 mV) at ±10 mA cm−2 in 1.0 M KOH, as well as a voltage of 1.52 V for overall water splitting. As revealed by in-situ Raman spectroscopy, on the one hand, Ni(OH)2 generated from Ni3S2 during alkaline HER accelerates water dissociation toward the gradually improved performance; on the other hand, this heterostructure undergoes extensive oxidation during OER, leading to excessive NiOOH covering on Ni3S2 and thereby declining activity. These changes are interpreted by the distinct thermodynamic relationship under specific electrochemical conditions via density functional theory calculations.

Promoting the water dissociation of nickel sulfide electrocatalyst through introducing cationic vacancies for accelerated hydrogen evolution kinetics in alkaline media

Developing cost-effective non-precious electrocatalysts with excellent HER performance in alkaline media is of significance for industrial hydrogen production. Herein, we successfully endow Ni3S2 with unprecedentedly enhanced alkaline HER activities by introducing nickel vacancies. The Ni3S2 catalyst with nickel vacancies exhibits an ultralow overpotential of 35 mV at 10 mA cm−2 in 1 M KOH electrolyte, outperforming commercial Pt/C (56 mV) and most reported non-precious electrocatalysts. The electron paramagnetic resonance and X-ray absorption fine structure etc. validates the formation of Ni vacancies and the change of the geometric/electronic structure of Ni3S2. Additionally, the theoretical calculations reveal that the Ni sites with higher valence state neighbouring the Ni vacancies can promote the water dissociation, playing a vital role in accelerating HER kinetics in alkaline media. This work may provide a universal strategy to enhance the HER activity of transition-metal compound catalysts in alkaline media by means of cationic defect engineering.

Thermal migration towards constructing W-W dual-sites for boosted alkaline hydrogen evolution reaction

Tungsten carbides, featured by their Pt-like electronic structure, have long been advocated as potential replacements for the benchmark Pt-group catalysts in hydrogen evolution reaction. However, tungsten-carbide catalysts usually exhibit poor alkaline HER performance because of the sluggish hydrogen desorption behavior and possible corrosion problem of tungsten atoms by the produced hydroxyl intermediates. Herein, we report the synthesis of tungsten atomic clusters anchored on P-doped carbon materials via a thermal-migration strategy using tungsten single atoms as the parent material, which is evidenced to have the most favorable Pt-like electronic structure by in-situ variable-temperature near ambient pressure X-ray photoelectron spectroscopy measurements. Accordingly, tungsten atomic clusters show markedly enhanced alkaline HER activity with an ultralow overpotential of 53 mV at 10 mA/cm2 and a Tafel slope as low as 38 mV/dec. These findings may provide a feasible route towards the rational design of atomic-cluster catalysts with high alkaline hydrogen evolution activity.

Boosted electrolytic hydrogen production at tailor-tuned nano-dendritic Ni-doped Co foam-like catalyst

Herein, the dynamic hydrogen bubble template (DHBT) method is used to design a microporous nano-dendritic Co film with foam-like morphology. Subsequently, Co film is doped by Ni and further electropassivated in 1.0 M KOH to develop metal/oxygenated metal interfaces, leading to a prompt water dissociation step in alkaline HER. The electropassivated nano-dendritic Ni-doped Co film is characterized by SEM, HR-TEM, XRD, EDS-mapping, ICP-OES, and XPS analyses. The electrochemical measurements show that the proposed electrocatalyst exhibits a striking activity, with an overpotential of −50 mV while operating at 10 mA cm-2, outperforming its precursors and surpassing/approaching the activity of benchmark and precious-metals-fabricated catalysts. Interestingly, the electropassivated Ni-doped Co film shows a marked enhancement towards the HER compared to the electropassivated Co film, indicating that the oxygenated Ni species play a crucial role by preserving the active metal/oxygenated metal interfaces. The obtained results introduce a promising robust catalytic material for electrolytic hydrogen production in alkaline media.

Stable and efficient hydrogen evolution reaction catalyzed by NiO-Rh2P heterostructure electrocatalyst

A NiO-Rh2P heterostructure electrocatalyst was constructed by phosphating the NiO-Rh structure. Due to the high capability of water dissociation by NiO, only 46 mV overpotential was demanded to achieve 10 mA cm−2 for the NiO-Rh2P, which is 73 mV lower than Rh2P in alkaline HER catalysis. Besides, the strong electronic interplay between NiO and Rh2P also contributed to the robust stability of NiO-Rh2P heterostructure electrocatalyst.

Sequential self-reconstruction of localized Mo species in hierarchical carbon/Co–Mo oxide heterostructures for boosting alkaline hydrogen evolution kinetics and durability

A hierarchical Co@NCNT/CoMoOx precatalyst is designed, and then a surface self-reconstruction process is deliberately induced, resulting in a superior alkaline HER performance with 600 h stability even in alkaline natural seawater.

Seamless separation of OHadand Hadon a Ni–O catalyst toward exceptional alkaline hydrogen evolution

Seamless separation of intermediates (OHadand Had) at the atomic scale is realized for exceptional alkaline HER activity on a Ni–O catalyst that is functionalized with low-coordinated oxygen and abundant vacancies.

Plasma-induced large-area N,Pt-doping and phase engineering of MoS2 nanosheets for alkaline hydrogen evolution

N2-plasma bombardment allows the large-area fabrication of high 1T phase N,Pt-doped MoS2 nanosheets with prominent alkaline HER activity.

Boosting the interfacial hydrogen migration for efficient alkaline hydrogen evolution on Pt-based nanowires

The interfacial hydrogen migration on binary Pt-based alloy nanowires is thermodynamically and kinetically boosted by P-doping to enhance the supply of dissociated hydrogen, resulting in a substantially improved alkaline HER.

Phase transition in V-doped cobalt hydroxide for a superior alkaline hydrogen evolution reaction.

Herein, V-doped cobalt hydroxides grown on carbon cloth (V-Co(OH)2/CC) were prepared via hydrothermal method. The incorporation of V can trigger phase transition and tune the local electronic structure of Co(OH)2, thereby improving the intrinsic alkaline HER activity. We find that the V-Co(OH)2 dominated by β-Co(OH)2 exhibits excellent HER activity with only 83 mV overpotential at a current density of 10 mA cm-2, which outperforms most reported hydroxide-based catalysts and even surpasses the commercial Pt/C at large current density (>160 mA cm-2).

TiO2-enhanced in situ electrochemical activation of Co3O4 for the alkaline hydrogen evolution reaction

In situ electrochemical activation results in high-valent metal compounds (with a composite of Co3O4 and TiO2 as a prototype) that exhibit outstanding catalytic performance in the alkaline HER.

Freestanding Surface Disordered NiCu Solid Solution as Ultrastable High Current Density Hydrogen Evolution Reaction Electrode

The poor performance of conventional powdery catalysts under large current density and the slow kinetics of the Volmer step limit the large-scale application of alkaline hydrogen generation. Here, we report the preparation of freestanding surface disordered NiCu solid solution as an ultrastable hydrogen evolution reaction electrode. The introduction of ammonium ion could tailor the reduction/nucleation rate of metal ions during the hydrothermal process, thus contributing to its unique intertwined 3D microstructure. The catalyst exhibits superior HER activity with an overpotential of 322 mV at 1000 mA cm-2, and limited degradation after 110 h continuous operation at 1000 mA cm-2. Density functional theory calculations confirm that the substitution of Cu could accelerate the hydroxyl desorption process (OHads + e- → OH-) and thereby enhance the overall kinetics of the Volmer step. Our work demonstrates the strong efficacy of optimizing catalysts' structures and facilitating intermediate desorption for boosting industrial-scale alkaline HER performance.

Hybridization of Mn/Ta bimetallic oxide and mesh-like porous bio-carbon for boosting copper reduction for D35/Y123-sensitized solar cells and hydrogen evolution

Developing high-performance and low-cost catalysts for replacing Pt-based catalysts is a significant challenge for solar cells and water splitting applications. In this work, a bifunctional hybrid catalyst of MnTa 2 O 6 @MPC (MPC: mesh-like bio-based porous carbon) was synthesized, using a co-precipitation approach. Benefiting from the high specific surface area (332.743 m 2 g −1 ), integrating the merits of the electrical conductivity of MPC, the outstanding electrocatalytic ability of MnTa 2 O 6 , and the synergistic effect between MnTa 2 O 6 and MPC, the catalytic activity of MnTa 2 O 6 @MPC was significantly enhanced. To boost the photovoltaic performance of dye-sensitized solar cells, a novel Cu 2+ /Cu + redox mediator and dye (Y123, D35) were adopted for replacing the traditional I 3 - /I - redox mediator and N719 dye, respectively. The resulting advanced solar cell with the Cu 2+ /Cu + redox mediator based on the MnTa 2 O 6 @MPC counter electrode catalyst exhibited a photovoltage of ~0.88 V, and cell efficiencies of 3.41% and 1.92% for the D35 and Y123 dye systems, respectively, which are respectively 16% and 8% higher than that of Pt. MnTa 2 O 6 @MPC also exhibited significant catalytic ability for hydrogen production, yielding a small overpotential of 141.9 mV at a current density of 10 mA cm −2 and a small Tafel slope of 105.0 mV dec −1 in an alkaline medium. This work provides promising guidance for designing bifunctional hybrid electrocatalysts for high-performance new energy devices. ● MnTa 2 O 6 @mesh-like porous carbon is prepared by a co-precipitation method. ● MnTa 2 O 6 @MPC is served as a bifunctional catalyst in DSSC and HER systems. ● Advanced DSSC with novel D35/Y123 dye and copper redox couple is fabricated. ● PCE of DSSCs (D35 dye) with MnTa 2 O 6 @MPC is 16% high than that of DSSCs with Pt. ● MnTa 2 O 6 @MPC obtained a low overpotential of 141.9 mV in alkaline HER.

Metal-polydopamine derived N-doped carbon nanorod wrapping Ni and Mo2C nanoparticles for efficient hydrogen evolution reaction

Herein, we have successfully synthesized a N-doped carbon nanorod, which is encapsulated with Ni and Mo2C nanoparticles (Ni/Mo2C/NC). It exhibits low onset-potential of 100 mV vs. RHE, an extremely small overpotential of 180 mV at 10 mA cm−2, a greatly reduced Tafel-slope of 63 mV dec−1 in 1 M KOH solution. The excellent alkaline HER activity of Ni/Mo2C/NC is attributed to the remarkable synergistic effects among Ni, Mo2C and NC. Active sites for water-splitting provided by Ni, the electron transfer from NC to Mo2C and the increased conductivity all make great contributions to enhance HER performance in alkaline pH.

Natural DNA-assisted ultrafine FeP embedded in N, P-codoped carbons for efficient oxygen reduction, hydrogen evolution and rechargeable zinc-air battery

The employment of Pt-based electrocatalysts in oxygen reduction and hydrogen evolution reactions (ORR/HER) have greatly frustrated the extensive proliferation of the relevant technologies and devices. Iron phosphide (FeP) was highlighted for an attractive Pt substitute benefitting from the richness and cheapness. Encapsulating FeP by doped carbon can endow the metal phase improved conductivity, durability and particularly enhanced catalytic activity by bilateral electronic coupling. Herein, by a facile one-pot strategy, natural DNA was first explored to prepare FeP embedded N, P-codoped carbon (NPC) composite with large surface areas, high graphitization and abundant high-quality dopants simultaneously. Strikingly, the long-chain DNA macromolecule confines the grown the of FeP to deliver the ultrafine but high crystalline nanoparticles. Thus, the newly-obtained FeP/NPC displays superior alkaline ORR performance comparable to Pt/C together with excellent alkaline HER activity. Density function theory computations reveal the interfacial electron transfer between FeP and NPC induces the optimal adsorption/desorption energies of key reaction intermediates on C sites adjacent to N for ORR and P sites of carbon for HER. The as-fabricated rechargeable zinc–air battery based on current FeP/NPC has large specific capacity and energy density with excellent charge-discharge stability, outperforming most of recently reported Fe-based counterparts.

Atomically Isolated Rh Sites within Highly Branched Rh2 Sb Nanostructures Enhance Bifunctional Hydrogen Electrocatalysis.

Breaking the bottleneck of hydrogen oxidation/evolution reactions (HOR/HER) in alkaline media is of tremendous importance for the development of anion exchange membrane fuel cells/water electrolyzers. Atomically dispersed active sites are known to exhibit excellent activity and selectivity toward diverse catalytic reactions. Here, a class of unique Rh2 Sb nanocrystals with multiple nanobranches (denoted as Rh2 Sb NBs) and atomically dispersed Rh sites are reported as promising electrocatalysts for alkaline HOR/HER. Rh2 Sb NBs/C exhibits superior HER performance with a low overpotential and a small Tafel slope, outperforming both Rh NBs/C and commercial Pt/C. Significantly, Rh2 Sb NBs show outstanding HOR performance of which the HOR specific activity and mass activity are about 9.9 and 10.1 times to those of Rh NBs/C, and about 4.2 and 3.7 times to those of Pt/C, respectively. Strikingly, Rh2 Sb NBs can also exhibit excellent CO tolerance during HOR, whose activity can be largely maintained even at 100 ppm CO impurity. Density functional theory calculations reveal that the unsaturated Rh sites on Rh2 Sb NBs surface are crucial for the enhanced alkaline HER and HOR activities. This work provides a unique catalyst design for efficient hydrogen electrocatalysis, which is critical for the development of alkaline fuel cells and beyond.

Natural DNA-derived highly-graphitic N, P, S-tridoped carbon nanosheets for multiple electrocatalytic applications

In the electrocatalytic oxygen reduction and hydrogen evolution reactions (ORR/HER), metal-free carbon-based materials presented great potentials as alternatives to Pt because of their flexible adjustability of electronic and geometric properties. The pursuit of high-performance carbons demand for high-level doping, large surface area and high graphitization, but the improvement of the former two aspects would inevitably impair the third one, which seems a contradictive proposition. Herein, by a facile “mix-and-pyrolyze” method, natural DNA was first developed to synthesize N, P, S-tridoped carbons (NPSC) with porous sheet structures, high graphitization, large surface areas and abundant high-quality dopants simultaneously. Thus, the newly-prepared NPSC displays superior alkaline ORR performance comparable to Pt/C together with excellent acidic activity and better stability. Meanwhile, NPSC is one of most active acidic HER catalysts and the best alkaline HER catalyst among carbon counterparts. Density function theory computation reveled the origins of superior performance are attributed to positively charged C sites neighboring to S for ORR and P sites for HER because of DNA-derived advantaged structural features. The as-fabricated rechargeable zinc–air battery based on current tridoped carbon has closed peak power density and specific capacity but much better charge–discharge stability compared with Pt/C.

Modulation of dual centers on cobalt-molybdenum oxides featuring synergistic effect of intermediate activation and radical mediator for electrocatalytic urea splitting

Construction of dual sites to break adsorption-energy scaling limitations offers an effective means of facilitating urea electrolysis for H 2 production, but a fundamental understanding of their synergistic mechanisms remains incomplete. Herein, we report a facile H 2 vapor-assisted strategy for the controllable fabrication of the bimetallic active Co 2 Mo 3 O 8 electrocatalyst for alkaline urea splitting, with an applied voltage of only 1.50 V required to deliver 50 mA cm −2 . Direct spectroscopic evidence and theoretical investigation demonstrate that the Co sites are responsible for the activation of intermediates, whereas the assisting Mo centers are identified as the OH or H radical mediators. Specifically, the synergistic effect of the Co–Mo dual sites was conclusively verified by the in-situ Raman and X­ray photoelectron spectroscopy. Theoretical calculations reveal that the short H-bonding (Mo-HO∙∙∙H–N amine CO–Co) and Co–C–N–Mo configuration formed at the Co–Mo bridge are the key features determining a high reactivity for urea oxidation. The accelerated reaction rate is attributable to the conversion of the endoergic CO 2 desorption to an exoergic reaction. In an alkaline H 2 evolution, Co atoms are the reaction sites for O–H bond cleavage of H 2 O, while Mo sites are considered to be the H 2 -evolving centers. Determination of the individual functionality of synergistic dual centers represents a critical step towards the rational design of highly-efficient electrocatalysts. • We report a facile H 2 vapor-assisted strategy for the fabrication of the Co 2 Mo 3 O 8 catalyst for the alkaline urea splitting. • In situ reconstructed Co 3 O 4 and high-valence Mo (VI) species on the surface are responsible for increased urea oxidation. • The short H-bonding and Co-C-N-Mo configuration are the key features determining a high reactivity for urea oxidation. • In an alkaline HER, Co atom accounts for cleavage of H-OH bond, while Mo site is identified as the H 2 -evolving center.

Eutectic molten salt assisted synthesis of highly defective and flexible ruthenium oxide for efficient overall water splitting

Designing and synthesizing efficient bifunctional electrocatalysts is of great significance for the application of overall water splitting but remains a great challenge. Herein, we synthesized low-crystallinity ruthenium oxides via a facile, eutectic molten salt-assisted method at low temperatures. Specifically, the optimized low-crystallinity RuO2-250 nanosheets with a highly defective structure and better structural flexibility showed both higher acidic OER and alkaline HER activity than commercial counterparts, reaching as low as 210 mV and 52 mV overpotentials at the current density of 10 mA cm−2 respectively. In situ Raman spectroscopy was employed to reveal the structural flexibility on the RuO2 catalyst during HER, which could contribute to its high activity. Furthermore, an electrolyzer with RuO2-250 catalyst requires only 1.57 V and 1.66 V cell voltage to achieve a current density of 10 mA cm−2 for overall water splitting under alkaline and acidic conditions respectively. This work provides a facile strategy for efficient design and preparation of low-crystalline materials and offers a new insight into the kinetic process of the water-splitting on ruthenium oxide.