HER Electrocatalysts Research Articles

Structure evolution and durability of Metal-Nitrogen-Carbon (M = Co, Ru, Rh, Pd, Ir) based oxygen evolution reaction electrocatalyst: A theoretical study

Developing low-cost, high activity and stability oxygen evolution reaction (OER) catalysts is significantly important but still challenging for water electrolyzers. In this work, we calculated the OER activity and stability of Metal-Nitrogen-Carbon (MNC, M = Co, Ru, Rh, Pd, Ir) based electrocatalyst with different structures (MN4C8, MN4C10, MN4C12) using density functional theory (DFT) method. These electrocatalysts were divided into three groups based on the value of ΔG*OH, that is ΔG*OH > 1.53 eV (PdN4C8, PdN4C10, PdN4C12), ΔG*OH < 1.23 eV (RuN4C8, RuN4C10, RuN4C12, CoN4C8, CoN4C10) and 1.23 eV < ΔG*OH < 1.53 eV (RhN4C8, RhN4C10, RhN4C12, IrN4C8, IrN4C10, IrN4C12, CoN4C12), and ΔG*OH determine whether the structure evolution will appear. The results proved that MNC (M = Rh, Ir) with 1.23 eV < ΔG*OH < 1.53 eV shows higher OER activity due to moderate binding energy between reaction intermediates and MNC. Furthermore, these catalysts could maintain MNC structure without further oxidation and structural evolution under working conditions (high temperature, dynamic condition, local electric field and strong specific adsorption), therefore show excellent stability. However, MNC electrocatalyst with ΔG*OH > 1.53 eV or ΔG*OH < 1.23 eV revealed less stability under working conditions, due to their low intrinsic stability or structural evolution under working conditions, respectively. In conclusion, we proposed a comprehensive evaluation method for MNC electrocatalysts by taking ΔG*OH as the screening criterion for OER activity and stability, as well as ΔEb under working condition as descriptor of stability. This is of great significance for the design and screening of ORR, OER and HER electrocatalysts under working conditions.

A new iron(II) complex as bi-functional electrocatalyst for hydrogen evolution reaction and hydrogen peroxide sensing

In this paper, a new Fe(II) complex, [FeCl2(BBP)]·(IPA)2 (BBP = 1,3-bis(1H-benzimidazole-2-yl)propane, IPA = isopropanol), was synthesized and characterized by single crystal X-ray diffraction, elemental analysis, IR and UV/Vis spectroscopy. The crystal analysis showed that the Fe(II) complex is mononuclear, and its Fe(II) center is four coordinate in a slightly distorted tetrahedron. The electrocatalytic activity towards HER and the electrochemical sensing performance to H2O2 of the Fe(II) complex was investigated by fabricating a composite electrode (a carbon paste electrode doped with the Fe(II) complex, Fe-CPE for short). Electrochemical studies have shown that the Fe-CPE only required a low overpotential of −0.481 V to drive the current density of 10 mA cm−2 with a smaller Tafel slope of 0.142 V dec−1 for HER in 0.5 M H2SO4 at 298 K. Additionally, Fe-CPE serves as a H2O2 sensor with superior electrocatalytic activity and a low detection limit of 0.36 μM (S/N = 3) in a linear range from 5.0 × 10−7 to 4.0 × 10−3 M in 0.5 M NaOH at −0.7 V. The above studies prove that the Fe(II) complex can be used as an effective bi-functional molecular electrocatalyst for HER and H2O2 sensing.

CoS2 with carbon shell for efficient hydrogen evolution reaction

In this study, we demonstrated the active electrocatalysts of CoS2 coated by N-doped carbon microspheres, CoS2@NHCs-x (x = 600, 700, 800, and 900; x is pyrolysis temperature). Results show that the obtained electrocatalyst has good catalytic activity and cyclic stability for the reaction of hydrogen evolution (HER) when the pyrolysis temperature is 800 °C. At a current density of 10 mA cm−2, the overpotential of CoS2@NHCs-800 was only 98 mV in 0.5 M H2SO4, and 118 mV in 1 M KOH, respectively. In addition, CoS2@NHCs-800 also revealed excellent electrochemical stability, with only 32.7% performance degradation after continuous reaction in 0.5 M H2SO4 for 20 h, and the later current density almost no longer deceased with time as the reaction process stabilized. The excellent HER catalytic performance of CoS2@NHCs-800 is mainly attributed to the rich active sites of CoS2, the unique porous core-shell structure, and the enhanced conductivity of the carbon carrier caused by N and S co-doping. This work opens up an opportunity for advanced CoS2-based electrocatalysts for HER.

Dense MoS2/CoS2 Heterointerfaces with Optimized Electronic Structure for Efficient Alkaline Hydrogen Evolution Reaction

Molybdenum disulfide (MoS2) is considered as a promising electrochemical catalyst for hydrogen generation. However, insufficient exposed active sites and poor conductivity severely impede its large-scale applications. Herein, the heterogeneous MoS2/CoS2 electrocatalyst was grown in situ on carbon cloth. The synergistic interaction between CoS2 and MoS2 occurring at the dense heterointerfaces grants the hybrid higher catalytic activities than single components, thereby speeding up hydrogen production rates. After annealing, the composite exhibits an ultralow overpotential of 67 mV at 10 mA cm–2 and a small Tafel slope of 70 mV dec–1 in 1 M KOH due to the improved conductivity and intimate connection between MoS2 and CoS2. Furthermore, it maintains an excellent cycle durability of 65 h without obvious attenuation at 20 mA cm–2. In-situ shielding tests reveal the main active sites coming from MoS2 rather than CoS2. On the basis of experimental measurements and theoretical calculations, CoS2 should work as the electron donor in the HER process and improve not only H2O adsorption but also H2 emission behaviors. The excellent hydrogen evolution performance of annealed-MoS2/CoS2/CC composite indicates that the present design is a prospective option for developing low-cost and efficient HER electrocatalysts in alkaline electrolytes.

Development of metal-organic framework-derived NiMo-MoO3−x porous nanorod for efficient electrocatalytic hydrogen evolution reactions

In this study, we developed a noble metal-free HER electrocatalyst NiMo-MoO3−x porous nanorod (NiMo-MoO3−x −PNR) by optimal thermal reduction of NiMoO4 porous nanorod (NiMoO4 −PNR), where the porous structure of NiMoO4 −PNR was enabled by calcining the designed Ni-Mo-metal-organic framework nanorod (Ni-Mo-MOF−NR). As a result of its ideal porous nanorod structure, composition, and improved bifunctional properties, the electrocatalyst demonstrated superior HER performance (a low overpotential of 24.5 mV @ 10.0 mA cm−2) in 1 м KOH, which was comparable with that of state-of-the-art platinum group metals (PGMs) based electrocatalysts. Furthermore, NiMo-MoO3−x −PNR displayed faster Volmer-Tafel mechanism (a small Tafel slope of 32 mV dec−1) for HER process. The superior HER activity of NiMo-MoO3−x −PNR was supported by density functional theory simulations. Moreover, it exhibited a high cyclic stability (unaffected after 100,000 cycles) and robust durability (102 h). Overall, this study demonstrates a simple, scalable, and versatile synthesis of a noble metal-free highly efficient inexpensive electrocatalyst for HER.

Metal-organic framework derived core-shell nanoparticles as high performance bifunctional electrocatalysts for HER and OER

Development of an affordable, stable, and efficient electrocatalyst using nonprecious material to generate green H2 and O2 is still a challenging research problem. This research demonstrates the development of an efficient bifunctional electrocatalyst for HER as well as OER. Self-sacrificial nickel-based MOF acted as a precursor in facile pyrolysis carried out at 600, 700, and 800 °C temperatures to yield three bifunctional electrocatalysts viz Ni@NCS-600, Ni@NCS-700, and Ni@NCS-800, respectively. A blend of metallic Ni-nanoparticles and heteroatoms (N, S, & O) doped graphitic matrix has shown a synergistic effect for efficient electrocatalysis. The facile transformation of Ni-MOF into core-shell structure imparts stability to metal electrocatalyst by preventing direct exposure to the electrolytes during water splitting. After systematic characterization by various analytical techniques, their electrocatalytic performances were evaluated for OER and HER in alkaline and acidic medium, respectively. Bifunctional electrocatalytic activity of Ni@NCS-800 was found to be highly efficient, and comparable to precious state-of-the-art catalysts (RuO2 and Pt/C). Ni@NCS-800 exhibits extremely low overpotential, which needs only 330 mV and 366 mV to reach 10 mAcm−2 current density in OER and HER, respectively. The Tafel slope has been derived from the EIS also, imparting the alternating current. Thereby, a superior electrokinetic activity of Ni@NCS-800 has been observed, due to the elimination of non-faradaic current, with a Tafel slope of 32 mV/dec. The stability was evaluated by potentiostatic and potentiodynamic techniques. Therefore, this study explores a suitable pathway for the fabrication of simple, nonprecious, stable, yet catalytically efficient material for HER and OER activity.

Engineering different B doping modes on Ru active sites for efficient alkaline hydrogen evolution

Two doping modes of B, direct doping on the Ru surface and doping into CNT, both modulate the electron density of Ru for high intrinsic activity, while the latter further improves charge transfer efficiency to accelerate reaction kinetics.

Screening Nickel-Doped Mo2 C Nanorod Arrays for Ultrastable and Efficient Hydrogen Evolution over a Wide pH Range.

Green hydrogen, using sustainable energy to decompose water to produce hydrogen, is regarded as the ideal and effective connection to convert electricity into chemical energy. Herein, well designed Ni-doped Mo2 C nanorod electrodes self-supported on three types of substrates (Ni foam, Cu foam and stainless steel wire mesh) with outstanding gas resistance and prominent corrosion resistance were assembled together to build up a wide pH applicable electrode for Hydrogen Evolution. In particular, Ni-doped Mo2 C nanorod arrays on stainless steel wire mesh donated as Ni-Mo2 C@SSW exhibited remarkable electrocatalytic properties towards hydrogen evolution reaction with superior overpotentials both in 1 M KOH and 0.5 M H2 SO4 (102 mV and 106 mV at the current density of 10 mA cm-2 ) and incomparable continuous durability. This work provides the possibility for the realization of low cost, high activity and ultra-stable durability HER electrocatalysts in practical industrial application.

Heterogeneous bimetallic Ni(OH)2-NiMoO4/NF as an efficient HER electrocatalyst for alkaline water splitting

As the climate warms and energy scarcity becomes increasingly severe, the search for greener and more sustainable energy sources has attracted widespread attention. This hierarchical dandelion-like structure catalyst exhibits excellent hydrogen evolution properties.

Mono-, bi- and tri-metallic platinum group metal-free electrocatalysts for hydrogen evolution reaction following a facile synthetic route

HER electrocatalysts were synthesized starting from metal-phthalocyanine. The higher pyrolysis temperature is beneficial and associated with the formation of nanoparticles. The addition of the second and third metal is also beneficial for HER.

Ni/NiO@NC as a highly efficient and durable HER electrocatalyst derived from nickel(II) complexes: importance of polydentate amino-acid ligands.

Research on Ni/NiO electrocatalysts has advanced significantly, but the main obstacles to their use and commercialization remain their relatively ordinary activity and stability. In this paper, a chelating structure based on the coordination of multidentate ligands and Ni(II) is proposed to limit the growth of Ni and Ni oxide grains. These features reduce the particle size of Ni/NiO, increase particle dispersion, and maintain the high activity and stability of the catalyst. Aspartic acid, as a polydentate ligand, could coordinate with Ni2+ to form structurally stable chelate rings. The latter can limit grain growth, but also coat the active core with thin carbon layers after calcination to further achieve the confinement and protection of nanoparticles. The hydrogen evolution overpotential of prepared nitrogen-doped graphitized carbon shells (Ni/NiO@NC) nanoparticles was 100 mV (vs. RHE) when the current density was 10 mA cm-2 in 1 M KOH. The hydrogen evolution overpotential increased by only 4 mV after 6000 continuous cyclic-voltammetry scans. Moreover, when coated on different conductive substrates, the overpotential of this catalyst dropped to 34.6 mV (vs. RHE) at a current density of 10 mV cm-2. The lowest overpotential of the composite was only 194.9 mV at a current density of 100 mA cm-2, which is comparable with that of noble metal-based electrocatalysts. This work provides a plausible method for designing high-performance electrocatalysts of small size.

Research progress of transition-metal dichalcogenides for the hydrogen evolution reaction

In this review, five common preparation methods of TMDs are summarized, and then the mechanisms of five regulatory strategies are analyzed from the perspective of density functional theory, suggesting the potential of TMDs as HER electrocatalysts.

Preparation of carbon coated hyperdispersed Ru nanoparticles supported on TiO2 HER electrocatalysts by dye-sensitization

A good HER catalyst C/Ru/TiO2 was prepared by the dye-sensitization method, Ru nanoparticles were uniformly loaded on TiO2, and the catalytic performance was further improved by carbon coating technology.

Strategically designed trimetallic catalyst with minimal Ru addresses both water dissociation and hydride poisoning barriers in alkaline HER

A highly active alkaline HER electrocatalyst (CoMoRu/CC) is prepared to achieve efficient water dissociation and consequently proton discharge with minimal Ru-content.

Rh for HER electrocatalysis? A critical analysis of recent studies and thoughts on the same!

An opinionated review presenting a critical analysis of the use of Rh as an HER electrocatalyst and the recent developments while highlighting the future directions of the same.

Orange-peel derived carbon-loaded low content ruthenium nanoparticles as ultra-high performance alkaline water HER electrocatalysts.

Carbon materials have a very wide range of applications in the field of electrocatalysis, both as catalyst bodies and as excellent supports for catalysts. In this work, we obtained a graphitic-like orange-peel derived carbon (OPC) material through pre-carbonization and KOH activation strategies using discarded orange-peel as a raw material. OPC has good graphitization characteristics and a few-layer structure, making it very suitable as a support for nanoparticle catalysts. In order to compare the performance of OPC, we used commercial graphene as the benchmark, made two carbon materials uniformly loaded with ruthenium nanoparticles under the same conditions, and obtained two HER catalysts (Ru/OPC and Ru/rGO). The results indicate that Ru/OPC has excellent HER catalytic performance under alkaline conditions, not only superior to Ru/rGO, but also surpassing commercial Pt/C. In 1 M KOH; the overpotential of Ru/OPC is only 3 mV at -10 mA cm-2, greatly exceeding those of Ru/rGO (100 mV) and Pt/C (31 mV). Under high current density (j), the performance of Ru/OPC is even better; the overpotential is 79 mV and 136 mV at -100 mA cm-2 and -200 mA cm-2, respectively. More importantly, Ru/OPC also has a very high TOF and long-term stability, with a TOF of up to 10.62 H2 s-1 at an overpotential of 100 mV and almost no attenuation after 72 h of operation at -50 mA cm-2. Ru/OPC also exhibits good catalytic performance under acidic conditions, significantly superior to that of Ru/rGO. For Ru/OPC, the overpotential is 86 mV, 167 mV and 214 mV at -10 mA cm-2, -100 mA cm-2 and -200 mA cm-2, respectively. Under the same conditions, the overpotential of Ru/rGO is 143 mV, 253 mV and 306 mV at -10 mA cm-2, -100 mA cm-2 and -200 mA cm-2, respectively.

Defect engineering in the MA2Z4 monolayer family for enhancing the hydrogen evolution reaction: first-principles calculations

The designed defect MA2Z4 monolayer family is highly activated toward HER electrocatalysts.

B, N-co-doped and C-coated Co2P composite derived from phytate derivatives as a high-efficiency HER electrocatalyst

The B, N-codoped C-coated Co2P (Co2P@BNC) exhibits low overpotential with a small Tafel slope (56 mV dec−1).

Development of inorganic-based nano-electrocatalysts for highly efficient water electrolysis

Polymer electrolyte membrane water electrolysis (PEMWE) is regarded as commercial electrochemical water-splitting technology to produce clean and sustainable hydrogen fuel from renewable energy resources. But current PEMWE system requires the noble metal-based metal, such as Pt, Ir or Ru, as electrocatalysts, which limits the large-scale commercialization of PEMWE. Thus, developing cost-effective and highly active electrocatalysts is important to produce hydrogen fuel on a large scale. In this paper, we introduce our recent works to develop inorganic-based noble-metal reduction or noble-metal-free nano-electrocatalysts for highly efficient water electrolysis through various facile synthetic strategies. First is Pt/MoC hybrid nanoparticles by hybridization of MoC and Pt nanoparticles for noble-metal-reduced HER electrocatalysts. Second is nickel and phosphorus substituted (Co1-xNix)(S1-yPy)2/Graphene ((Co1-xNix)(S1-yPy)2/G) 3D nano-architecture, which consist of self-assembly of 2D nanosheet, by structure-engineering and composition-engineering. Thrid is CoP nanosheets which are self-supported on carbon fabric current collector.

In-situ “encapsulation” of Mo:Mo2C with nano-mosaic structure on wood-derived carbon for hydrogen evolution reaction

Coupling metallic and Mo2C phases uniformly on conductive matrix at nanoscale is a promising route to solve the poor electrical conductivity and aggregation problems of nano-Mo2C. In this work, a 3D self-supporting carbonized wood (CW) electrode encapsulation with mosaic structure Mo:Mo2C for hydrogen evolution reaction was fabricated successfully by a facile annealing treatment and a gas-solid reaction. The presence of Mo phase accelerated the transfer rate of electrons and provided heterogeneous interface. The obtained electrode shows abundant catalytic active sites and low electrochemical impedance, thus improving the catalytic process of splitting water for HER. The Mo:Mo2C-775 electrode requires an overpotential of 73.5 mV and 117 mV to achieve the current density of 10 mA cm−2 in 0.5 M H2SO4 and 1.0 M KOH, respectively. Moreover, Mo:Mo2C-775 electrode displayed excellent stability performance, which almost maintained a constant current density for 12 h (at −100 mV vs RHE) in 0.5 M H2SO4 and 1.0 M KOH, respectively. This study provides a new idea for preparation of efficient 3D self-supporting electro-catalyst for HER.