Non-precious Metal Electrocatalysts Research Articles

Synergistic promotion of the oxygen evolution reaction by Co and Fe dual-doping of NiS2

Bimetallic doped Co,Fe–NiS2 nanosheet arrays are a promising non-precious metal electrocatalyst for the oxygen reduction reaction (OER).

Constructing oxygen vacancies by doping Mo into spinel Co3O4 to trigger a fast oxide path mechanism for acidic oxygen evolution reaction

The development of non-precious metal electrocatalysts for acidic oxygen evolution reaction (OER) that are highly durable, cost-effective, and efficient is crucial to advancing the use of proton exchange membrane water electrolyzers (PEMWEs).

(Invited) Durable Hybrid Electrocatalysts for Fuel Cells

Proton exchange membrane fuel cell converts hydrogen and oxygen into electricity with zero emission. The high cost and low durability of Pt-based electrocatalysts for oxygen reduction reaction hinder its wide applications. The development of non-precious metal electrocatalysts also reaches the bottleneck because of the low activity and durability. Here we rationally design a hybrid electrocatalyst consisting of atomically dispersed Pt and Fe single atoms and Pt-Fe alloy nanoparticles. The Pt mass activity of the hybrid catalyst is 3.7 times higher than that of commercial Pt/C in a fuel cell. More importantly, the fuel cell with an ultra-low Pt loading in the cathode (0.015 mgPt cm-2) shows excellent durability, with 97 % activity retention after 100,000 cycles and no noticeable current drop at 0.6 V for over 200 h. These results highlight the importance of the synergistic effects among active sites in hybrid electrocatalysts and provide an alternative way to design more active and durable low-Pt electrocatalysts for electrochemical devices.

Phosphorus-doped synergy of phase change in heterogeneous catalysts of NiS–NiS2 for efficient electrocatalysis of Pb(II)

A fundamental understanding of the electroanalytical activity of transition metal sulfide electrocatalysts, especially the origin of the electrocatalytic reactivity on the surface sites of heterostructures with multiple crystalline phases, is essential for the design of low-cost and highly efficient nonprecious metal electrocatalysts for further scientific and technological achievements. Herein, we injected P into NiS and occupied the S sites through a doping strategy. The redistributed electronic structure induced the construction of heterostructures, which significantly improved the structure and chemical state of electrochemically inert NiS. The phase-change mechanism between NiS and NiS2 synergistically catalyzes Pb(II), while the P and S sites jointly lose electrons. Moreover, the constructed heterojunction sensor shows the a sensitivity of 83.43 μA μM−1 to Pb(II) with a theoretical limit of detection of 48 nM, as well as excellent stability, reproducibility, and anti-interference ability. The accurate detection in real water further reveals the potential of this sensor for practical applications. This study provides a guiding strategy for improving electrochemically inert materials to design highly active electrocatalytic interfaces, which has important implications for the development of highly efficient electrode-sensitive materials similar to precious metals to achieve accurate electrical analysis.

Bimetallic nitride Co3W3N nanoparticles anchored on ordered N-Doped porous Carbon: An efficient catalyst for oxygen reduction reaction

Carbon-supported transition metal nitrides (TMNs/C) have been considered as promising non-precious metal electrocatalysts toward oxygen reduction reaction (ORR) in both fuel cells and metal–air batteries. However, the development of TMNs/C catalysts with high-performance by using simple and efficient synthesis is still a significant challenge. Here, an in-situ multi-constituents co-assembly strategy was applied to fabricate a novel carbon-supported bimetallic nitride Co3W3N composite, in which Co3W3N nanoparticles (NPs) uniformly anchored in N-doped ordered porous carbon (NPC). Within Co3W3N/NPC composite, the homogeneously dispersed Co3W3N NPs (∼9 nm) combined with N-doping possess highly ORR catalytic activity. its ordered mesoporous structure provides a three-dimensional conductive network and a high surface area (591.9 m2 g−1), which ensures fast electron transport and effective electrolyte infiltration. Due to the superiorities of material and structure, the Co3W3N/NPC served as ORR electrocatalyst shows almost the same excellent electrocatalytic activity with commercial Pt/C in alkaline media. Especially, its durability and methanol-tolerance ability in the ORR process are much better than those of commercial Pt/C. Furthermore, Co3W3N/NPC composite can also be used as cathodic catalyst of Li-O2 battery, which exhibits good rate capability and cycling stability.

Carbon Nanotube-Encased FeNi Alloy/N-Doped Carbon ORR Catalyst: High Efficiency and Stability

The efficient reduction of oxygen in fuel cell technology using platinum group metals (PGMs) faces challenges like sluggish kinetics, high costs, and poor durability. To overcome these limitations, PGM-free oxygen reduction reaction (ORR) electrocatalysts are sought after. Transition-metal-based electrocatalysts, specifically metal-nitrogen co-doped carbon (M-N/C, M = Fe, Co, etc.), have emerged as promising alternatives due to their abundant pore structures, high surface area, conductivity, and cost-effectiveness. This review explores various non-precious metal electrocatalysts for ORR, highlighting pyrolyzed transition metal nitrogen-containing complexes on carbon (M–Nx/C) as outstanding candidates, with Fe-N/C demonstrating remarkable performance. In this study, we introduce a novel approach to construct Fe-Nx doped large-diameter carbon nanotubes (Fe,Ni-N/C) by pyrolyzing zeolitic imidazolium frameworks-8 (ZIF-8) functionalized with nickel acetate. This approach capitalizes on strong intercalation between acetate and metal ions, promoting Fe-Nx active site formation while generating large-diameter carbon nanotubes. The resulting catalyst facilitates rapid mass transport and maximizes active site exposure, nearing the performance of Pt/C. Our catalyst exhibits an initial potential of 1.03 V, a half-wave potential of 0.88 V, and a limit current of 5.5 mA cm−2. Remarkably, it retains 85.7% of its initial performance in a 36,000 s chronoamperometry test, demonstrating superior durability and methanol toxicity resistance compared to Pt/C. Large-diameter carbon nanotubes offer a potential alternative electrocatalyst, eliminating the need for templates, simplifying mass production for applications like sensors, supercapacitors, and lithium-ion batteries. Furthermore, our Fe,Ni-N/C catalyst outperforms commercial Pt/C, making it a promising choice for ORR applications in fuel cells.

Triggering efficient reconstructions of Co/Fe dual-metal incorporated Ni hydroxide by phosphate additives for electrochemical hydrogen and oxygen evolutions

Alkaline electrochemical water splitting has been considered as an efficient way for the green hydrogen production in industry, where the electrocatalysts play the critical role for the electricity-to-fuel conversion efficiency. Phosphate salts are widely used as additives in the fabrication of electrocatalysts with improved activity, but their roles on the electrocatalytic performance have not been fully understood. Herein, we fabricate Co, Fe dual-metal incorporated Ni hydroxide on Ni foam using NaH2PO4 ((Co, Fe)NiOxHy-pi) and NaH2PO2 ((Co, Fe)NiOxHy-hp) as additive, respectively. We find that (Co, Fe)NiOxHy-hp with NaH2PO2 in the fabrication shows high activity and stability for both HER and OER (a overpotential of −0.629 V and 0.65 V at 400 mA cm−2 for HER and OER, respectively). Further experiment reveals that the reconstructed structures of electrocatalyst by using NaH2PO2 (hp) endow high electrocatalytic performances: (1) in-situ generated active metal improves the accumulation, transportation and activity of hydrogen species in the HER process; and (2) in-situ generated poor-crystalline hydroxide endows superior charge/mass transportation and kinetics improvements in the OER process. Our study may provide an insightful understanding on the catalytic performance of non-precious metal electrocatalysts by controlling additives and guidance for the design and synthesis of novel electrocatalysts.

Rational design of bimetal phosphide embedded in carbon nanofibers for boosting oxygen evolution

The development of non-precious metal electrocatalysts for oxygen evolution reaction (OER) is crucial for generating large-scale hydrogen through water electrolysis. In this work, bimetal phosphides embedded in electrospun carbon nanofibers (P-FeNi/CNFs) were fabricated through a reliable electrospinning–carbonization–phosphidation strategy. The incorporation of P-FeNi nanoparticles within CNFs prevented them from forming aggregation and further improved their electron transfer property. The bimetal phosphides helped to weaken the adsorption of O intermediate, promoting the OER activity, which was confirmed by the theoretical results. The as-prepared optimized P-Fe1Ni2/CNFs catalyst exhibited very high OER electrocatalytic performance, which required very low overpotentials of just 239 and 303 mV to reach 10 and 1000 mA cm−2, respectively. It is superior to the commercial RuO2 and many other related OER electrocatalysts reported so far. In addition, the constructed alkaline electrolyzer based on the P-Fe1Ni2/CNFs catalyst and Pt/C delivered a cell voltage of 1.52 V at 10 mA cm−2, surpassing the commercial RuO2||Pt/C (1.61 V) electrolyzer. It also offered excellent alkaline OER performance in simulated seawater electrolyte. This demonstrated its potential for practical applications across a broad range of environmental conditions. Our work provides new ideas for the ration design of highly efficient non-precious metal-based OER catalysts for water electrolysis.

An efficient Fe2Se3/Fe2O3 heterostructure electrocatalyst for oxygen evolution reaction

In this study, novel iron-based electrocatalysts, including Fe2Se3, Fe2O3, and Fe2Se3/Fe2O3 heterostructures, have been developed to bring down overpotential in the oxygen evolution reaction (OER). Among these, the Fe2Se3/Fe2O3 heterostructure emerges as a highly promising electrocatalyst for OER, offering exceptional efficiency, cost-effectiveness, and minimal overpotential. The Fe2Se3/Fe2O3 electrocatalyst exhibits outstanding electrochemical performance, with a remarkable onset potential of 1.31 V (vs. RHE) and a minimum 160 mV overpotential at 20 mA/cm2 for OER. Notably, this prepared electrocatalyst demonstrates the lowest overpotential when compared to benchmark Fe-based OER electrocatalysts. Furthermore, during controlled potential electrolysis at 1.65 V (vs. RHE), the electrocatalyst maintains a stable current density of 65 mA/cm2, highlighting its impressive electrochemical robustness. The hydrothermal synthesis method used for the synthesis of Fe2Se3, Fe2O3, and their heterostructure is particularly very simple and straightforward. Which making them excellent candidates for water splitting applications, particularly in OER. These significant achievements accomplished through the utilization of non-precious metal electrocatalysts, open up new possibilities for practical OER implementations. Undoubtedly, these findings will greatly benefit the scientific community in the development of efficient electrocatalysts using non-noble metals for the electrochemical water splitting process.

Bottom-up self-assembly strategy to construct ternary MoxC/Ni3Fe@GL as efficient water splitting electrocatalyst

Efficient and robust bifunctional non-precious metal electrocatalysts, used for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), are crucial to develop water splitting commercial applications. Herein, a bottom-up self-assembly strategy is proposed to construct ternary electrocatalysts of nitrogen-doped graphene-like carbon layers encapsulated MoxC (x = 1, 2) and Ni3Fe alloy nanoparticles (MoxC/Ni3Fe@GL) for efficient water electrolysis. The optimized sample (0.27MoxC/Ni1.5Fe@GL, 0.27 represent the mass of ammonium molybdate in the precursor) requires overpotentials (η10) of 88 and 150, 265 mV in 0.5 M H2SO4 for HER and 1.0 M KOH for HER and OER, respectively. Furthermore, as a bifunctional electrocatalyst in a two-electrode cell, 0.27MoxC/Ni1.5Fe@GL requires only 1.523 V at 10 mA cm−2, which surpasses the noble metal RuO2(+)||Pt/C(−) in 1.0 M KOH electrolyte, and shows excellent stability by working at 20 mA cm−2 long as 150 h. The superior electrocatalytic performance can mainly originate from MoxC and Ni3Fe alloys synergistically effected results. The partial doping of Ni or Fe atoms into Mo2C optimizes the electronic structure, making the intrinsic activity enhanced. On the other hand, the incorporation of MoxC heterophases effectively inhibits the Ni3Fe nanoparticles agglomeration, benefitting to expose more active sites. Moreover, the protection of encapsulated thin N-doped graphene-like carbon layers for the nanoparticles against corrosion, guarantees the long-time durability. This work provides a potential general bottom-up self-assembly approach to construct high-performance electrocatalysts with multiphase heterostructures with enriched abundant active sites and enhanced intrinsic activity for energy coversion fields.

Well-defined Ni3N nanoparticles armored in hollow carbon nanotube shell for high-efficiency bifunctional hydrogen electrocatalysis

Alkaline H2-O2 fuel cells and water electrolysis are crucial for hydrogen energy recycling. However, the sluggish kinetics of the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) in an alkaline medium pose significant obstacles. Thus, it is imperative but challenging to develop highly efficient and stable non-precious metal electrocatalysts for alkaline HOR and HER. Here, we present the intriguing synthesis of well-defined Ni3N nanoparticles armored within an N-doped hollow carbon nanotube shell (Ni3N@NC) via the conversion of a hydrogen-bonded organic framework (HOF) to metal-organic framework (MOF), followed by high-temperature pyrolysis. As-developed Ni3N@NC demonstrates exceptional bifunctionality in alkaline HOR/HER electrocatalysis, with a high HOR limiting current density of 2.67 mA cm−2 comparable to the benchmark 20 wt% Pt/C, while achieving a lead in overpotential of 145 mV and stronger CO-tolerance. Additionally, it achieves a low overpotential of 21 mV to attain a HER current density of 10 mA cm−2 with long-term stability up to 340 h, both exceeding those of Pt/C. Structural analyses and electrochemical studies reveal that the remarkable bifunctional hydrogen electrocatalytic performance of Ni3N@NC can be ascribed to the synergistic coupling among the well-dispersed small-sized Ni3N nanoparticles, chain-mail structure, and optimized electronic structure enabled by strong metal-support interaction. Furthermore, theoretical calculations indicate that the high-efficiency HOR/HER observed in Ni3N@NC is attributed to the strong OH− affinity, moderate H adsorption, and enhanced water formation/dissociation ability of the Ni3N active sites. This work underscores the significance of rational structural design in enhancing performance and inspires further development of advanced nanostructures for efficient hydrogen electrocatalysis.

Synergistic d-p hybridized Co/W5N4 heterostructure catalyst for industrial alkaline water/seawater hydrogen evolution

Developing efficient and durable non-precious metal electrocatalysts with industrial current density is urgent for hydrogen evolution reaction from alkaline water/seawater but remains challenging. Here, a heterostructured Co/W5N4 catalyst with porous structure is innovatively constructed. The theoretical calculations confirm the strong d-p hybridization between Co and N at the interface of Co/W5N4 with the modulation of d‐band center of Co sites. The synergistic effect between Co and W5N4 is disclosed that H2O can rapidly dissociate on the W sites to generate H* adsorbed at the Co sites for favorable H2 production. Consequently, the Co/W5N4 catalyst affords low overpotentials of 113 and 118 mV to drive current density of 100 mA cm−2 in alkaline water/seawater electrolytes, respectively, which are even superior to those of commercial Pt/C. More importantly, it can also present outstanding HER stability at large current density of 500 mA cm−2 for over two weeks (350 h) in alkaline water/seawater electrocatalysis.

PW6Mo6/ZIF-67@NF composite with exposed Co nodes as efficient oxygen evolution reaction electrocatalyst

The construction of efficient, sustainable, and low-cost nonprecious metal electrocatalysts for oxygen evolution reaction (OER) is necessary for the realization of electrocatalytic overall water splitting. Herein, the PW6Mo6/ZIF-67@NF is prepared using a simple coprecipitation method. Characterization results indicate that the PW6Mo6 induces the exposure of Co nodes in ZIF-67, which can act as catalytic active sites for OER. Meanwhile, the introduction of PW6Mo6 improves the conductivity and electrochemical active surface area of ZIF-67, which further enhances the OER performance. The electrochemical test results show that the PW6Mo6/ZIF-67@NF exhibit an ultralow overpotential of 201 mV at 10 mA cm−2 and a small Tafel slope of 55 mV dec−1 for OER, which is lower than that of ZIF-67@NF (329 mV, 286 mV dec−1). Our study demonstrates the potential of polyoxometalate and ZIF composites to decrease the barriers of OER and provides a feasible approach for exploring economical and practical electrocatalysts.

Construction of transition metal/metal oxide synergistic with carbon nanomaterials trinity composites to promote electrocatalytic oxygen evolution

Novel non-precious metal electrocatalysts replace precious metal catalysts for water separation and are highly anticipated in commercial applications. The coexistence of crystalline and amorphous phases is thought to facilitate efficient electrocatalytic activity. In this work, a facile strategy is proposed to induce crystalline-amorphous core-shell nanocomposites via direct-current (DC) arc plasma technology. Heterogeneous crystalline amorphous nanocomposites (Fe/MnO@C) formed by coupling transition metal manganese oxide and magnetic iron into a carbon matrix exhibit excellent water oxidation properties. Spin-pinning effect is formed at the ferromagnetic metal/antiferromagnetic manganese oxide interface by controlled surface reconstruction. The established spin pinning effect can reduce the kinetic barriers in the OER (oxygen evolution reaction). The optimized Fe/MnO@C nanocomposite can be applied for OER in pH-universal electrolytes with low overpotential and small Tafel slope. The synergistic effects in an advantageous crystalline-amorphous core-shell nanocomposite significantly boost the reaction dynamics for water splitting. This research may shed light on the construction of high performance and low cost non-precious metal electrocatalysts for water oxidation.

Enhanced electrocatalytic glycerol oxidation on CuCoN0.6/CP at significantly reduced potentials

Electrocatalytic alcohol oxidation coupled with the hydrogen evolution reaction, wherein a thermodynamically favorable oxidation reaction replaces the sluggish kinetics of the oxygen evolution reaction, has recently attracted considerable attention. However, the development of nonprecious-metal electrocatalysts capable of delivering much lower oxidation potentials holds great significance. In this study, we proposed and developed CuCoN0.6 nanowires loaded on conductive carbon paper (denoted as CuCoN0.6/CP) as an efficient catalyst for selective glycerol oxidation to formate. Our catalyst achieved a remarkably high faradic efficiency of 90.0% towards formate production. More notably, it required an anode potential as low as 1.07 V to achieve a current density of 10 mA cm−2, a significantly lower potential than that reported in the literature. Experimental characterizations reveal that the oxidations of Cu+ and Co2+ ions promoted the formation of reactive hydroxyl species, which are responsible for the substantially reduced oxidation potential and enhanced glycerol oxidation performance. Furthermore, we investigated the reaction pathway of glycerol oxidation and structural changes in the catalysts. The catalyst reconstruction led to the formation of CoOOH, which is considered as the active site for glycerol oxidation. Finally, we successfully separated high-purity and value-added potassium diformate product. This work not only advances the electrocatalytic conversion of biomass-derived alcohols but also provides insights into the design of electrocatalysts with broad applications.

Engineering Mn–Nx sites on porous carbon via molecular assembly strategy for long-life zinc-air batteries

Nitrogen-coordinated manganese atoms on carbon materials denoted as MnNC, serve as the highly active non-precious metal electrocatalysts for oxygen reduction reaction (ORR) in zinc-air batteries (ZABs). Nonetheless, a significant challenge arises from the tendency of Mn atoms to aggregate during heat treatment, thereby compromising ORR performance in ZABs. In this work, the molecular assembly strategy based on the hydrogen bond interaction was employed to fabricate the MnNC electrocatalyst. This approach promotes the dispersion of Mn atoms, creating abundant Mn–Nx active sites. Furthermore, the resulting three-dimensional porous nanostructure, formed by molecular assembly, significantly enhances accessibility to the Mn–Nx active sites. The porous nanostructure not only shortens the diffusion path of reactants and charges but also improves mass transfer. The MnNC exhibits impressive ORR catalytic performance with a half-wave potential of 0.90 V (vs. RHE). The liquid-type ZAB based on MnNC displays a high specific capacity of 816.6 mAh/g and an extended charge–discharge cycle life of 1000 h. Quasi-solid-state ZAB based on MnNC can operate stably for 24 h. This work presents an effective strategy to synthesize transition metal-nitrogen-carbon (MNC) electrocatalysts tailored for long-life zinc-air battery.

NiCo-layered double hydroxides /Co9S8 with heterogeneous structure as ultra-high performance electrocatalyst for oxygen evolution reaction

Heterogeneous interface engineering is an ideal method for designing low-cost and efficient electrocatalysts for oxygen evolution reaction (OER). NiCo-layered double hydroxide (LDH)/Co9S8 with heterogeneous structure was prepared by a two-step hydrothermal method and employed for OER. The layered structure with a spherical base exhibited the lower overpotential (151 mV) and Tafel slope (100 mV dec−1) at a current density of 10 mA cm−2, which surpass commercially available IrO2 and most reported non-precious metal electrocatalysts. The synergistic effect at the interface can increase the conductivity of the material, induce electron migration between NiCo-LDH and Co9S8, and decrease the energy barrier of the OER intermediate, thereby increasing the electrocatalytic activity. At the same time, heterostructures with rough surfaces and ultra-hydrophilic properties can provide the desired stability, promote ion penetration and the release of bubbles, improve the accessibility of the active site, and thus enhance the catalytic performance of OER. This work provides a feasible way to develop high performance OER electrocatalysts.

Fe and Zn Addition Effects of Ti Oxide-Based Electrocatalyst on Catalytic Activity for Oxygen Reduction Reaction

The conventional catalyst of polymer electrolyte fuel cell (PEFC) is a platinum which is categorized as precious metal with very high-cost material, and its performance is limited in principal. From this point of view, the non-precious metal electrocatalyst should be required. We have focused and studied group 4 and 5 metal oxide-based electrocatalyst as non-platinum catalysts for the oxygen reduction reaction (ORR) because of low-cost, abundant reserves, and high stability in acidic electrolytes [1-2]. We found that titanium oxide prepared from TiOTPyzPz supported on multi-walled carbon nanotubes had superior ORR activity [3]. On the other hand, it was published as an international patent that the addition of other elements such as Fe and Ni is affected to enhance the ORR activity of Ti oxide-based electrocatalyst [4]. We have also applied for the TiOTPyzPz as a starting material with Fe, Ni, and Zn addition to enhance the ORR activity of Ti oxide-based electrocatalyst [5-6]. In this study, we have investigated the addition effects of Zn and Fe for Ti oxide-based electrocatalyst on the catalytic activity for the ORR.2,3-Dicyanopyrazine, urea, and Ti isopropoxide were dissolved in quinoline and refluxed to synthesize TiOTPyzPz. Iron acetate and zinc acetate were also added to dissolve in quinoline to obtain the Fe and Zn-added TiOTPyzPz as a starting material. These starting materials were mixed with carbon nanotube by ball-milling to prepare the precursors. These precursors were heat-treated under low oxygen partial pressure at 900 oC for 3 h to obtain the oxide-based electrocatalyst powder. The catalyst powder was dispersed into 1-propanol with Nafion solution to prepare a catalyst ink. The ink was dropped on a glassy carbon rod to use as a working electrode in electrochemical measurement.Electrochemical measurements were performed in 0.5 mol dm-3 H2SO4 at 30 oC with a conventional 3-electrode cell. A reversible hydrogen electrode (RHE) and a glassy carbon plate were used as used as a reference and counter electrode, respectively. Slow scan voltammetry (SSV) was performed at a scan rate of 5 mV s-1 from 0.2 V to 1.2 V vs. RHE under O2 and N2. The ORR current (i ORR) was determined by calculating the difference between the current under O2 and N2.Figure 1 shows the ORR polarization curves Fe and/or Zn addition to the Ti oxide-based electrocatalysts. The Fe and Zn added Ti oxide-based electrocatalyst (Fe,Zn-TiOx) was obviously the highest activity for the ORR, and it was higher ORR activity than Fe added Ti oxide-based electrocatalyst (Fe-TiOx), Zn added Ti oxide-based electrocatalyst (Zn-TiOx), and Ti oxide-based electrocatalyst (TiOx) without addition. It reveals that the addition of Fe and Zn was found to be effective for enhancing the ORR activity, and Fe addition was more effective than Zn addition for enhancing the ORR activity. XRD pattern of TiOx shows several peaks identified TiO2-Rutile and TiC0.3N0.7 while the XRD pattern of Fe-TiOx, Zn-TiOx, and Fe,Zn-TiOx also shows several peaks identified similar to TiOx. According to results from ICP analysis, the contain amount of Ti and Fe in Fe,Zn-TiOx was similar to preparation amount in precursor, but that of Zn showed below detection limit. From SEM images, Zn-TiOx and Fe,Zn-TiOx have more space in its powder than Fe-TiOx and TiOx. Based on above results, it is suggested that Zn addition affected to increased electrochemical surface area of TiOx, and Fe addition affected to form active site [7] in TiOx as similar case as Zr oxide-based electrocatalyst [8].Acknowledgement: The authors thank New Energy and Industrial Technology Development Organization (NEDO) and ENEOS Tonen General Research / Development Encouragement & Scholarship Foundation for financial support.Reference A. Ishihara, Y. Ohgi, K. Matsuzawa, S. Mitsushima, and K. Ota, Electrochim. Acta, 55, 8005 (2010).A. Ishihara, S. Tominaka, S. Mitsushima, H. Imai, H. Imai, O. Sugino, and K. Ota, Curr. Opin. Electrochem., 21 , 234 (2020).S. Tominaka, A. Ishihara, T. Nagai, and K. Ota, ACS Omega, 2, 5209 (2017).K. Takahashi, T. Imai, R. Monden, Y. Wakisaka, and S. Sato, Oxygen Reduction Catalyst, Process for Producing Same, and Polymer Electrolyte Membrane Fuel Cell, WO/2013/008501.K. Matsuzawa, M. Obata, Y. Takeuchi, Y. Ohgi, K. Ikegami, T. Nagai, R. Monden and A. Ishihara, ECS Trans., 108(7), 181 (2022).K. Matsuzawa, M. Obata, Y. Takeuchi, Y. Ohgi, K. Ikegami, T. Nagai, R. Monden and A. Ishihara, ECS Trans., 108(7), 189 (2022).J-H. Kim, A. Ishihara, S. Mitsushima, N. Kamiya, and K. Ota, Acta, 52, 2492 (2007).Y. Takeuchi, K. Watanabe, K. Matsuzawa, T. Nagai, K. Ikegami, R. Monden, and A. Ishihara, Chem. Lett., 51, 927 (2022). Figure 1

(Digital Presentation) Structure-Activity Relationship of M-N-C Electrocatalysts Synthesized Using a General Solution-Phase Coordination Approach

Metal- and nitrogen-doped carbon (M-N-C) catalysts have great potential in heterogeneous catalysis. They are used to catalyze various crucial electrochemical reactions, such as the oxygen reduction reaction (ORR), the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and the CO2 reduction reaction (CO2RR).1-4 The nitrogen-coordinated metal sites (MNx) have been considered the main active sites in these M-N-C catalysts. However, the synthesis of MNx moieties often undergoes a high-temperature heat-treatment step, resulting in low site density. On the other side, the coordination environment in the MNx sites is also affected by the metal species which induced the site formation. Therefore, it is challenging to single out the role of central metal in the structure-activity relationships for these MNx sites.In this presentation, we will discuss our recent progress in the development of a solution-phase coordination synthesis approach targeting M-N-C catalysts with high active-site density and well-defined coordination environments.5, 6 A series of M-N-C catalysts are synthesized via this approach by coordinating electroactive target metal ions with the nitrogen-coordinated metal-vacancy (MVNx) sites in N-C templated by sacrificial metals. With a combined experimental and computational approach, we explore the role of sacrificial metals, including s-, p-, 3d-, 4d-, and f-block metals, in forming various MVNx sites with unique coordination configurations. The structure-activity relationship between the coordination environment and the catalytic activity for ORR, HER, OER, and CO2RR is established by comparing the MNx site structures induced by various sacrificial metals. Furthermore, we will present the activity series of metal centers in M-N-C catalysts with the same and well-defined coordination environment for ORR, HER, OER, and CO2RR. These results will guide the future development of M-N-C catalysts. Acknowledgments Financial support from the State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences is greatly appreciated. This study is financially supported by the Shanxi Province grant (Grant No. 20210302123011, 202203021212007, and 202103021224442), and Key Research and Development (R&D) Projects of Shanxi Province (202102070301018). References J. Cui, Q. Chen, X. Li and S. Zhang. Recent advances in non-precious metal electrocatalysts for oxygen reduction in acidic media and PEMFCs: an activity, stability and mechanism study. Green Chemistry, 23, 6898 (2021).H. He, H. H. Wang, J. Liu, X. Liu, W. Li and Y. Wang. Research Progress and Application of Single-Atom Catalysts: A Review. Molecules, 26, 6501 (2021).U. Martinez, S. Komini Babu, E. F. Holby, H. T. Chung, X. Yin and P. Zelenay. Progress in the Development of Fe-Based PGM-Free Electrocatalysts for the Oxygen Reduction Reaction. Advanced Materials, 31, 1806545 (2019).Y. Wang, X. Cui, L. Peng, L. Li, J. Qiao, H. Huang and J. Shi. Metal–Nitrogen–Carbon Catalysts of Specifically Coordinated Configurations toward Typical Electrochemical Redox Reactions. Advanced Materials, 33, e2100997 (2021).M. Huang, R. Ding, J. Yang, W. Shi, S. Shi, L. Chen, S. Liu and X. Yin. Formation of Nitrogen-Coordinated Metal Sites (M = Fe, Co) via Solution-Phase Coordination on Nickel- And Nitrogen-Co-Doped Carbon Templates with Metal Vacancy-Nx Sites. Journal of The Electrochemical Society, 169, 106507 (2022).M. Huang, L. Chen, R. Ding, W. Shi, Q. Qin, J. Yang, S. Liu and X. Yin. Solution-Phase Synthesis of Co-N-C Catalysts Using Alkali Metals-Induced N-C Templates with Metal Vacancy-Nx sites. ChemRxiv, doi: 10.26434/chemrxiv-2022-xnh88 (2022).

Unexpected Potential Dependent HER Behaviors of Cationic Phosphorus Doped WO3 Nanosheets

TMOs are generally considered as catalytically inert for hydrogen evolution reaction (HER).[1] This unique property has promoted a wide variety of applications of TMOs, such as aqueous-based lithium ionic batteries, electrochromic smart windows, electrocatalysts and/or catalyst supports. However, hydrogen evolution as an undesired side reaction is commonly observed when they are used in aqueous-based supercapacitors and battery applications.[2] The unexpected HER mechanism for intrinsic TMOs has not been studied until very recently by McKone and Mpourmpakis groups.[3] With careful theoretical calculations, they clearly demonstrated that intrinsic WO3 is not HER active. Bulk hydrogen (H) intercalation into WO3 is a prerequisite for its catalytic activity toward HER. Applying electrochemical potential to WO3 primarily sets the bulk H stoichiometry of thus formed hydrogen bronzes HxWO3. The level of intercalation (x), precisely to say, the density of the intercalated hydrogen in the WO3, in turn determines the formation of W-H*, the bonding strength of W-H*, and their consumption to H2 (HER). Significant HER is only seen at potentials negative enough when x > 0.5. Beyond this intercalation level, HER is no longer dictated by potential-dependent activation energies, instead, is controlled by the density of the hydrogen intercalation on the surface of WO3 catalysts. In line with this extensive theoretical study, Augustyn group very recently experimentally demonstrated the dependence of HER activity of WO3 materials on their electrochemical insertion characteristics.[4] By including crystal water between the WO3 sheets, proton intercalation is greatly facilitated likely with a Grotthuss mechanism. Accordingly, the HER kinetics is largely improved with a large positive shift of the HER on-set potential. On the other hand, by inclusion of molecular pillars in the WO3 lattice to physically block proton intercalation, the HER activity of WO3 was largely inhibited. Recently, we developed a facile approach to cationically dope WO3 nanosheets with red phosphorus. The proton interaction and the associated HER behavior as a function of electrochemical potentials were carefully studied with multiple electrochemical techniques. Interestingly, we found that proton interaction is largely suppressed even without including molecular pillars in the P-doped WO3 lattice. At lower intercalation levels before the so-called “potential independent regime”, the HER kinetics is largely decreased, as expected, compared to the non-doped WO3 control sample. While in the “potential independent regime”, the HER kinetics is largely enhanced. Furthermore, including alkaline metal ions into the electrolyte, the HER kinetics is further suppressed as demonstrated by largely negatively shifted onset potentials and the increased Tafel slopes. Interestingly, in the “potential independent regime”, the HER kinetics is further drastically enhanced. Extensive structural characterization and theoretical calculations are undergoing to reveal the mechanism behind these interesting tunable potential dependent - proton interaction and HER behavior, which will be reported in this work. Understanding how heteroatomic doping could modulate proton interaction and HER behaviors of TMOs at atomic levels would provide practical guidance for designing more efficient and selective electrochemical catalysts for various catalytic reduction reactions, such as carbon dioxide reductions and nitrogen/nitrate reductions to valuable compounds.[1] Zhang, S.; Zhang, X.; Rui, Y.; Wang, R.; Li, X., Recent advances in non-precious metal electrocatalysts for pH-universal hydrogen evolution reaction. Green Energy & Environment 2021, 6 (4), 458-478.[2] Wang, R.; Mitchell, J. B.; Gao, Q.; Tsai, W.-Y.; Boyd, S.; Pharr, M.; Balke, N.; Augustyn, V., Operando Atomic Force Microscopy Reveals Mechanics of Structural Water Driven Battery-to-Pseudocapacitor Transition. ACS Nano 2018, 12 (6), 6032-6039.[3] Miu, E. V.; McKone, J. R.; Mpourmpakis, G., The Sensitivity of Metal Oxide Electrocatalysis to Bulk Hydrogen Intercalation: Hydrogen Evolution on Tungsten Oxide. Journal of the American Chemical Society 2022, 144 (14), 6420-6433.[4] Spencer, M. A.; Fortunato, J.; Augustyn, V., Electrochemical proton insertion modulates the hydrogen evolution reaction on tungsten oxides. The Journal of Chemical Physics 2022, 156 (6), 064704. Figure 1