Earth-abundant Catalysts For Hydrogen Evolution Reaction Research Articles

Polyaniline nanowires decorated nickel phosphides hollow spheres hydrogen evolution catalyst for proton exchange membrane electrolysis

Cost-competitive proton exchange membrane water electrolyzer (PEMWE) requires efficient and earth-abundant electrocatalyst to replace Platinum for hydrogen evolution reaction (HER). We report here a polyaniline (PANI) nanowires decorated Ni2P hollow spheres catalyst and its exceptional activity toward HER in 0.5 M H2SO4 aqueous and PEMWE. The excellent catalytic activity of HER originates from unique hybrid structure of PANI/Ni2P with good conductivity, decent surface activity and optimal porous property. As a cheaper alternative to Pt/C, we used PANI/Ni2P as the cathode to set a PEMWE cell (Nafion® 117 membrane), the cell showed a current density of 1.0 A cm−2 at 1.822 V and 2.0 A cm−2 at 2.026 V, which is comparable with Pt/C (1.778 V at 1.0 A cm−2, and 2.086 V at 2.0 A cm−2). Our catalyst maintained a stable performance in a PEM electrolysis at a current density of 1.0 A cm−2 with the temperature of 80 °C, and preserved surface morphology and electron state well after 320 h continuous electrolysis. This study offers PANI/Ni2P HER catalyst as a cheaper replacement for Pt/C in PEMWE and provides a new insight to design earth-abundant catalysts for HER.

Establishing stability of the novel layered ternary tri-chalogenide materials: Emergence of a new generation of earth abundant HER catalysts

Energetic and structural stability of thirteen novel ternary transition metal tri-chalcogenide layers, claimed to be promising catalysts for hydrogen evolution reaction (HER), are studied. Detailed analyses of electronic structure, and mechanical and phonon properties establish that ten out of the thirteen materials are stable. Further analyses establish that these are chemically in the same class as the known layered ternary transition metal tri-chalcogenide materials. These lead us to claim that it should be possible to synthesize these materials experimentally, thus enlarging the list of candidate materials that can replace platinum as HER catalysts.

Ultrastable molybdenum disulfide-based electrocatalyst for hydrogen evolution in acidic media

Despite the incredible success in reducing the overpotential of nonprecious catalysts for acidic hydrogen evolution reaction (HER) in the past few years, the stability of most platinum-free electrocatalysts is still poor. Here, we report an ultrastable electrocatalyst for acidic HER based on two-dimensional (2D) molybdenum disulfide (MoS2) doped with trace amount of palladium (<5 μg cm−2), which creates sulfur vacancies (S-vacancies). The optimized catalyst shows stable operation over 1000 h at 10 mA cm−2 with overpotential of 106 mV. The MoS2 catalyst is stabilized on a defective vertical graphene support, where the strong interaction at the 2D-2D interface increases the adhesion between the catalyst and the support. Palladium (Pd) doping generates rich sulfur vacancies in MoS2 that have a twofold role: (1) increasing hydrogen adsorption energy, which enhances activity; and (2) further increasing the adhesion between graphene support and defective MoS2, and thus enhancing stability. Complementary theoretical studies reveal the reaction pathways for substitutional doping, where the Mo-vacancy sites are prior to be doped by Pd. Our work thus offers a strategy for making stable, efficient, and earth-abundant HER catalysts with strong potential to replace platinum for PEM electrolysis.

Stabilizing sulfur vacancy defects by performing "click" chemistry of ultrafine palladium to trigger a high-efficiency hydrogen evolution of MoS2.

Defect engineering is widely applied in transition metal dichalcogenides to produce high-purity hydrogen. However, the instability of vacancy states on catalysis still remains a considerable challenge. Here, our first-principles calculations showed that, by optimizing the asymmetric S vacancy in the highly asymmetric 1T' crystal of layered bitransition metal dichalcogenides (Co-MoS2) in light of Pd modulation, the relative amount of metastable phase and the quantity of active sites in the structure can be reduced and increased, respectively, leading to a further boosted hydrogen evolution reaction (HER) activity toward layered bi-transition metal dichalcogenides. Thus, we then used a "click" chemistry strategy to make such a catalyst with engineered unsaturated sulfur edges via a strong coupling effect between ultrafine Pd ensembles and Co-MoS2 nanosheets. As expected, the Pd-modulated Co-MoS2 nanosheets exhibited a very low overpotential of 60 mV at 10 mA cm-2 with a small Tafel slope (56 mV dec-1) for the HER in 1.0 M PBS, comparable to those of commercial Pt/C. In addition, their high HER activity was retained in acidic and alkaline conditions. Both the theoretical and experimental results revealed that Pd ensembles can efficiently activate and stabilize the inert basal plane S sites during HER processes as a result of the formation of Pd-S in Co-MoS2. This work not only provides a deeper understanding of the correlation between defect sites and intrinsic HER catalytic properties for transition metal chalcogenide (TMD)-based catalysts, but also offers new insights into better designing earth-abundant HER catalysts displaying high efficiency and durability.

Boosting Hydrogen Transfer during Volmer Reaction at Oxides/Metal Nanocomposites for Efficient Alkaline Hydrogen Evolution

Developing efficient and robust Earth-abundant hydrogen evolution reaction (HER) catalysts is crucial for the scalable and sustainable production of hydrogen. This study builds on the promising concept of oxide/metal nanocomposites, namely NiO/Ni, by incorporating another metal (in this case, Mo) into NiO to tune the adsorption energy of hydrogen (H). Theoretical and experimental approaches are combined to design Mo-NiO/Ni nanocomposites for efficient HER in alkaline media. The incorporation of Mo into NiO weakens the adsorption of H, favoring its transfer to nearby Ni active sites to accelerate the Volmer reaction, and also stabilizes the crystal structure of NiO. The Mo-NiO/Ni catalyst exhibits a 50 mV overpotential at a current density of −10 mA cm–2 with a Tafel slope of 86 mV dec–1, indicating that it is one of the most promising alkaline HER electrocatalysts reported to date. These findings suggest design principles for inexpensive, efficient, and high-performance Earth-abundant HER catalysts.

Enhancing Durability and Photoelectrochemical Performance of the Earth Abundant Ni-Mo/TiO2 /CdS/CIGS Photocathode under Various pH Conditions.

Cu(In,Ga)(S,Se)2 (CIGS) is a promising photocathode material owing to its high absorption coefficient, adjustable band gap, and suitable band edge for the hydrogen evolution reaction (HER). However, most CIGS photocathodes have suffered from instability in applications that require a wide range of pH conditions and have utilized noble metal HER catalysts to achieve a high performance. Thus, improving the durability of the CIGS photocathode under various pH conditions and developing a cost-effective non-noble metal catalyst are critical issues in the photoelectrochemical (PEC) application of this promising photocathode material. Here, we catalyze the CIGS photocathode with Ni-Mo as a non-noble metal to enhance the PEC efficiency, and we employ atomically grown TiO2 to passivate the CdS/CIGS surface and improve the stability under a wide range of pH conditions. Our Ni-Mo alloy exhibits the best HER catalytic activity among reported earth-abundant HER catalysts in both acidic and alkaline solutions. The Ni-Mo/CdS/CIGS photocathode yields an onset potential of 0.5 V (vs. RHE) and a short-circuit photocurrent density as high as 15-25 mA cm-2 under various pH conditions ranging from 0.4 to 14, which is highly comparable to that of Pt/CdS/CIGS. Furthermore, the passivation of CdS/CIGS with a thin TiO2 layer, obtained by atomic layer deposition, effectively prevents the photocorrosion of CdS and the dissolution of the Mo back contact, which are the main causes of the degradation of the photocathode. The optimized Ni-Mo/TiO2 /CdS/CIGS photocathode produces a stable photocurrent density at 0 VRHE for 100 minutes except under strong alkaline conditions. The current work presents a very useful method to improve the efficiency and durability of the CIGS photocathodes with an earth-abundant metal catalyst, which completely replaces Pt.

Sponge-like nickel phosphide–carbon nanotube hybrid electrodes for efficient hydrogen evolution over a wide pH range

Cost-effective hydrogen production via electrolysis of water requires efficient and durable earth-abundant catalysts for the hydrogen evolution reaction (HER) over a wide pH range. Herein, we report sponge-like nickel phosphide–carbon nanotube (Ni x P/CNT) hybrid electrodes that were prepared by facile cyclic voltammetric deposition of amorphous Ni x P catalysts onto the threedimensional (3D) porous CNT support. These compounds exhibit superior catalytic activity for sustained hydrogen evolution in acidic, neutral, and basic media. In particular, the Ni x P/CNT electrodes generate cathodic currents of 10 and 100 mA·cm−2 at overpotentials of 105 and 226 mV, respectively, in a 1 M phosphate buffer solution (pH = 6.5) with a Tafel slope of 100 mV·dec−1; the currents were stable for over 110 h without obvious decay. Our results suggest that the 3D porous CNT electrode supports could serve as a general platform for earth-abundant HER catalysts for the development of highly efficient electrodes for hydrogen production.