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Chinese Journal of Catalysis
2021, Vol. 42, No. 8
Online: 18 August 2021

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Cover:  Prof. Abhishek Dey and co-workers demonstrated that with suitable design of Fe porphyrin catalyst, it is realized to selectively reduce proton to hydrogen even in the presence of oxygen at the cost of charge consumption for oxygen reduction reaction. Read more about the article behind the cover on pages 1327–1331.

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Editorial

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Preface to Special Issue on Water Splitting, from Molecular to Material Rui Cao, Hai-Long Jiang 2021, 42 (8):  1239-1240.  DOI: 10.1016/S1872-2067(20)63774-3 Abstract ( 119 )   HTML ( 145 )   PDF (420KB) ( 400 )

Reviews

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Recent progress in production and usage of hydrogen peroxide Shunichi Fukuzumi, Yong-Min Lee, Wonwoo Nam 2021, 42 (8):  1241-1252.  DOI: 10.1016/S1872-2067(20)63767-6 Abstract ( 330 )   HTML ( 29 )   PDF (2019KB) ( 732 )   Hydrogen peroxide has attracted increasing interest as an environmentally benign and green oxidant that can also be used as a solar fuel in fuel cells. This review focuses on recent progress in production of hydrogen peroxide by solar-light-driven oxidation of water by dioxygen and its usage as a green oxidant and fuel. The photocatalytic production of hydrogen peroxide is made possible by combining the 2e– and 4e– oxidation of water with the 2e– reduction of dioxygen using solar energy. The catalytic control of the selectivity of the 2e– vs. 4e– oxidation of water is discussed together with the selectivity of the 2e– vs. 4e– reduction of dioxygen. The combination of the photocatalytic 2e– oxidation of water and the 2e– reduction of dioxygen provides the best efficiency because both processes afford hydrogen peroxide. The solar-light-driven hydrogen peroxide production by oxidation of water and by reduction of dioxygen is combined with the catalytic oxidation of substrates with hydrogen peroxides, in which dioxygen is used as the greenest oxidant.

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O-O bond formation mechanisms during the oxygen evolution reaction over synthetic molecular catalysts Xue-Peng Zhang, Hong-Yan Wang, Haoquan Zheng, Wei Zhang, Rui Cao 2021, 42 (8):  1253-1268.  DOI: 10.1016/S1872-2067(20)63681-6 Abstract ( 520 )   HTML ( 43 )   PDF (1480KB) ( 719 )   Water oxidation is one of the most important reactions in natural and artificial energy conversion schemes. In nature, solar energy is converted to chemical energy via water oxidation at the oxygen-evolving center of photosystem II to generate dioxygen, protons, and electrons. In artificial energy schemes, water oxidation is one of the half reactions of water splitting, which is an appealing strategy for energy conversion via photocatalytic, electrocatalytic, or photoelectrocatalytic processes. Because it is thermodynamically unfavorable and kinetically slow, water oxidation is the bottleneck for achieving large-scale water splitting. Thus, developing highly efficient water oxidation catalysts has attracted the interests of researchers in the past decades. The formation of O-O bonds is typically the rate-determining step of the water oxidation catalytic cycle. Therefore, better understanding this key step is critical for the rational design of more efficient catalysts. This review focuses on elucidating the evolution of metal-oxygen species during transition metal-catalyzed water oxidation, and more importantly, on discussing the feasible O-O bond formation mechanisms during the oxygen evolution reaction over synthetic molecular catalysts.

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Recent developments in the use of single-atom catalysts for water splitting Yao Wang, Xun Huang, Zidong Wei 2021, 42 (8):  1269-1286.  DOI: 10.1016/S1872-2067(20)63619-1 Abstract ( 296 )   HTML ( 18 )   PDF (5135KB) ( 705 )   Electrochemical water splitting is regarded as the most promising approach to produce hydrogen. However, the sluggish electrochemical reactions occurring at the anode and cathode, namely, the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), respectively, consume a tremendous amount of energy, seriously hampering its wide application. Recently, single-atom catalysts (SACs) have been proposed to effectively enhance the kinetics of these two reactions. In this minireview, we focus on the recent progress in SACs for OER and HER applications. Three classes of SACs have been reviewed, i.e., alloy-based SACs, carbon-based SACs and SACs supported on other compounds. Different factors affecting the activities of SACs are also highlighted, including the inherent element property, the coordination environment, the geometric structure and the loading amount of metal atoms. Finally, we summarize the current problems and directions for future development in SACs.

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Amorphous nanomaterials in electrocatalytic water splitting Chengying Guo, Yanmei Shi, Siyu Lu, Yifu Yu, Bin Zhang 2021, 42 (8):  1287-1296.  DOI: 10.1016/S1872-2067(20)63740-8 Abstract ( 261 )   HTML ( 10 )   PDF (6878KB) ( 820 )   Electrochemical water splitting, as a promising method for hydrogen production, has attracted significant attention. However, the lack of an electrocatalyst with a small energy loss and fast reaction kinetics has hindered the development of this technology. Amorphous nanomaterials with short-range order and long-range disorder features have recently shown superior activity compared to their crystalline counterparts in water electrolysis. The enhanced activity arising from their intrinsic disordered structure results in more active sites and a higher intrinsic activity of such sites. In this regard, this review is aimed at summarizing the progress in amorphous electrocatalysts for water splitting. First, the synthesis strategies for amorphous electrocatalysts are discussed. Characterization tools for amorphous nanomaterials are then summarized. Moreover, the origin of the enhanced activity and stability of amorphous nanomaterials is analyzed. Finally, the current challenges and promising opportunities in this research area are discussed. This review aims to provide a guide for designing and developing amorphous nanomaterials with a fascinating electrocatalytic water splitting performance.

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Recent developments of nanocarbon based supports for PEMFCs electrocatalysts Junwei Chen, Zuqiao Ou, Haixin Chen, Shuqin Song, Kun Wang, Yi Wang 2021, 42 (8):  1297-1326.  DOI: 10.1016/S1872-2067(20)63736-6 Abstract ( 380 )   HTML ( 20 )   PDF (5716KB) ( 616 )   Nanocarbons, widely and commonly used as supports for supported Pt-based electrocatalysts in PEMFCs, play a significant role in Pt dispersion and accessibility, further determining their corresponding electrocatalytic performance. This paper provides an overview of the nanoarchitectures and surface physicochemical properties of nanocarbons affecting the electrocatalyst performance, with an emphasis on both physical characteristics, including pore structure, and chemical properties, including heteroatom doping and functional carbon-based supports. This review discusses the recent progress in nanocarbon supports, guides the future development direction of PEMFC supports, and provides our own viewpoints for the future research and design of PEMFCs catalysts, advancing the commercialization of PEMFCs.

Communications

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Proton reduction in the presence of oxygen by iron porphyrin enabled with 2 nd sphere redox active ferrocenes Biswajit Mondal, Pritha Sen, Abhishek Dey 2021, 42 (8):  1327-1331.  DOI: 10.1016/S1872-2067(20)63761-5 Abstract ( 174 )   HTML ( 9 )   PDF (1741KB) ( 307 )   Supporting Information Hydrogen evolution in the presence of atmospheric level of oxygen is a significant barrier in the quest for an alternative, sustainable and green source of energy to counter the depleting fossil fuel sources and increasing global warming due to fossil fuel burning. Oxygen reduction is thermodynamically more favourable than proton reduction and it often produces reactive oxygenated species upon partial reduction which deactivates the catalyst. Thus, catalyst development is required for efficient proton reduction in the presence of oxygen. Here, we demonstrate an iron porphyrin having triazole containing 2 nd sphere hydrogen bonding residues appended with redox active ferrocene moieties (α4-Tetra-2-(3-ferrocenyl-1,2,3-triazolyl)phenylporphyrin (FeFc4)) as a bifunctional catalyst for fast and selective oxygen reduction to water and thus, preventing the proton reduction by the same catalyst from oxidative stress. Fe(0) is the active species for proton reduction in these iron porphyrin class of complexes and it is observed that the kinetics of proton reduction at Fe(0) state occurs at much faster rate than O2 reduction and thus, paving the way for selective proton reduction in the presence of oxygen.

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Odd-membered cyclic hetero-polyoxotitanate nanoclusters with high stability and photocatalytic H2 evolution activity Ya-Jie Liu, Lin Geng, Yao Kang, Wei-Hui Fang, Jian Zhang 2021, 42 (8):  1332-1337.  DOI: 10.1016/S1872-2067(20)63648-8 Abstract ( 123 )   HTML ( 13 )   PDF (1261KB) ( 369 )   Supporting Information We investigated the hydrolysis of TiIV along with naturally abundant AlIII ions and reported the formation of a stable and semiconducting nanocluster. Interestingly, this compound exhibits an unusual odd-membered ring structure and also represents the largest Al-containing polyoxotitanium cluster (PTC) observed thus far. The presence of a shell of organic ligands as well as the incorporation of hetero-Al III ions endowed the nanocluster with high air, thermal, and pH stabilities. The present compound exhibited a record photocatalytic hydrogen evolution of 402.88 μmol g -1 h -1 among PTC materials. This work not only paves the way towards stable PTC materials but also provides new insights into the design of novel photocatalysts.

Articles

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Buffer anion effects on water oxidation catalysis: The case of Cu(III) complex Qifa Chen, Haoyi Du, Mingtian Zhang 2021, 42 (8):  1338-1344.  DOI: 10.1016/S1872-2067(20)63729-9 Abstract ( 137 )   HTML ( 12 )   PDF (1390KB) ( 403 )   Water oxidation is the bottleneck of artificial photosynthesis. Since the first ruthenium-based molecular water oxidation catalyst, the blue dimer, was reported by Meyer’s group in 1982, catalysts based on transition metals have been widely employed to explore the mechanism of water oxidation. Because the oxidation of water requires harsh oxidative conditions, the stability of transition complexes under the relevant catalytic conditions has always been a challenge. In this work, we report the redox properties of a CuIII complex (TAML-CuIII) with a redox-active macrocyclic ligand (TAML) and its reactivity toward catalytic water oxidation. TAML-CuIII displayed a completely different electrochemical behavior from that of the TAML-CoIII complex previously reported by our group. TAML-CuIII can only be oxidized by one-electron oxidation of the ligand to form TAML•+-CuIII and cannot achieve water activation through the ligand-centered proton-coupled electron transfer that takes place in the case of TAML-CoIII. The generated TAML•+-CuIII intermediate can undergo further oxidation and ligand hydrolysis with the assistance of borate anions, triggering the formation of a heterogeneous B/CuOx nanocatalyst. Therefore, the choice of the buffer solution has a significant influence on the electrochemical behavior and stability of molecular water oxidation catalysts.

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Incorporating porphyrin-Pt in light-harvesting metal-organic frameworks for enhanced visible light-driven hydrogen production Huihui Hu, Lingzhen Zeng, Zhe Li, Tianbao Zhu, Cheng Wang 2021, 42 (8):  1345-1351.  DOI: 10.1016/S1872-2067(20)63738-X Abstract ( 194 )   HTML ( 94 )   PDF (1008KB) ( 601 )   Supporting Information Molecular catalysts for H2-evolution are of interest for their integration into light-harvesting complexes for photocatalytic water splitting. Here, we report the meso-tetra (4-carboxyphenyl) porphine [(TCPP)Pt II] complex as a molecular H2-evolving photocatalyst using chloranilic acid (CA) as a sacrificial electron donor, the choice of which is critical to the stability of the photocatalyst. When triethanolamine was used, [(TCPP)Pt II] decomposed to form Pt nanoparticles. Density functional theory calculations together with evidence from electrochemical and spectroscopic analyses suggested that the catalysis was possibly initiated by a proton-coupled electron transfer (PCET) to form [(TCPP)Pt I]-N-H, followed by another electron injection and protonation to form a [(TCPP)Pt II-hydride]-N-H intermediate that can release H2. As the whole catalytic cycle involves the injection of multiple electrons, a light-harvesting network should be helpful by providing multiple photo-induced electrons. Thus, we integrated this molecular catalyst into a light-harvesting metal-organic framework to boost its activity by ~830 times. This work presents a mechanistic study of the photocatalytic H2 evolution and energy transfer and highlights the importance of a light-harvesting network for multiple electron injections.

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Dye-sensitized photoanode decorated with pyridine additives for efficient solar water oxidation Jiayuan Li, Yong Zhu, Fei Li, Guoquan Liu, Suxian Xu, Licheng Sun 2021, 42 (8):  1352-1359.  DOI: 10.1016/S1872-2067(20)63683-X Abstract ( 101 )   HTML ( 9 )   PDF (1111KB) ( 381 )   Splitting water into hydrogen and oxygen by dye-sensitized photoelectrochemical cell (DSPEC) is a promising approach to solar fuels production. In this study, a series of pyridine derivatives as surface additives were modified on a molecular chromophore and water oxidation catalyst co-loaded TiO2 photoanode, TiO2|RuP, 1 (RuP = Ru(4,4′-(PO3H2)2-2,2′-bipyridine)(2,2′-bipyridine)2, 1 = Ru(bda)(L)2, (bda = 2,2′-bipyridine-6,6′-dicarboxylate, L = 10-(pyridin-4-yloxy)decyl)phosphonic acid). The addition of pyridine additives was found to result in up to 42% increase in photocurrent. Under simulated sun-light irradiation, TiO2|RuP, 1, P1 (P1 = 4-Hydroxypyridine) produced a photocurrent density of 1 mA/cm 2 at a bias of 0.4 V vs. NHE in acetate buffer. Moreover, the observed photocurrents are correlated with the electron-donating ability of the substituent groups on pyridine ring. Transient absorption measurements and electrochemical impedance spectroscopy revealed that surface-bound pyridine can effectively retard the back-electron transfer from the TiO2 conduction band to the oxidized dye, which is a major process responsible for energy loss in DSPECs.

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Fe/Co and Ni/Co-pentlandite type electrocatalysts for the hydrogen evolution reaction Mathias Smialkowski, David Tetzlaff, Lars Hensgen, Daniel Siegmund, Ulf-Peter Apfel 2021, 42 (8):  1360-1369.  DOI: 10.1016/S1872-2067(20)63682-8 Abstract ( 215 )   HTML ( 14 )   PDF (1894KB) ( 563 )   Supporting Information Metal-rich transition metal sulfides recently gained increasing attention as electrocatalysts for the hydrogen evolution reaction (HER), as they are capable to overcome major challenges faced by sulfide-rich metal catalysts such as limited conductivity and the necessity of nanostructuring. Herein, we present the synthesis, characterization and electrocatalytic investigation of ternary metal-rich sulfide composites FexCo9‒xS8 as well as NiyCo9‒yS8 (x = y = 0-4.5), which possess pentlandite-type structures. In this study, we show a stepwise alteration of the binary cobalt pentlandite Co9S8 and report on the replacement of cobalt with up to 4.5 equivalents of either iron or nickel. These altered pentlandite composites facilitate the proton reduction in acidic media at different temperatures. We furthermore show that the stoichiometric variation has a decisive influence on the electrochemical activation/deactivation behavior of the catalysts under reductive electrocatalytic conditions. Here, Co-deficient composites display an improved HER performance in contrast to Co9S8. Notably, Ni/Co compounds generally tend to show higher catalytic activities towards HER than their respective Fe/Co compounds.

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In situ formation of amorphous Fe-based bimetallic hydroxides from metal-organic frameworks as efficient oxygen evolution catalysts You Xu, Kaili Ren, Rong Xu 2021, 42 (8):  1370-1378.  DOI: 10.1016/S1872-2067(20)63741-X Abstract ( 144 )   HTML ( 9 )   PDF (3041KB) ( 673 )   Supporting Information Oxygen evolution from water driven by electrocatalysis or photocatalysis poses a significant challenge as it requires the use of efficient electro-/photo-catalysts to drive the four-electron oxygen evolution reaction (OER). Herein, we report the development of an effective strategy for the in situ chemical transformation of Fe-based bimetallic MIL-88 metal-organic frameworks (MOFs) into corresponding bimetallic hydroxides, which are composed of amorphous ultrasmall nanoparticles and afford an abundance of catalytically active sites. Optimized MOF-derived NiFe-OH-0.75 catalyst coated on glassy carbon electrodes achieved a current density of 10 mA cm ‒2 in the electrocatalytic OER with a small overpotential of 270 mV, which could be decreased to 235 mV when loading the catalysts on a nickel foam substrate. Moreover, these MOF-derived Fe-based bimetallic hydroxides can be used as efficient cocatalysts when combined with suitable photosensitizers for photocatalytic water oxidation.

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In situ synthesis of a nickel boron oxide/graphdiyne hybrid for enhanced photo/electrocatalytic H2 evolution Xue-Peng Yin, Shu-Wen Luo, Shang-Feng Tang, Xiu-Li Lu, Tong-Bu Lu 2021, 42 (8):  1379-1386.  DOI: 10.1016/S1872-2067(20)63601-4 Abstract ( 134 )   HTML ( 12 )   PDF (1154KB) ( 392 )   Supporting Information Developing highly active catalysts for photo/electrocatalytic water splitting is an attractive strategy to produce H2 as a renewable energy source. In this study, a new nickel boron oxide/graphdiyne (NiBi/GDY) hybrid catalyst was prepared by a facile synthetic approach. Benefitting from the strong electron donating ability of graphdiyne, NiBi/GDY showed an optimized electronic structure containing lower valence nickel atoms and demonstrated improved catalytic performance. As expected, NiBi/GDY displayed a high photocatalytic H2 evolution rate of 4.54 mmol g ‒1 h ‒1, 2.9 and 4.5 times higher than those of NiBi/graphene and NiBi, respectively. NiBi/GDY also displayed outstanding electrocatalytic H2 evolution activity in 1.0 M KOH solution, with a current density of 400 mA/cm 2 at an overpotential of 478.0 mV, which is lower than that of commercial Pt/C (505.3 mV@400 mA/cm 2). This work demonstrates that GDY is an ideal support for the development of highly active catalysts for photo/electrocatalytic H2 evolution.

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Role of transition-metal electrocatalysts for oxygen evolution with Si-based photoanodes Rajender Boddula, Guancai Xie, Beidou Guo, Jian Ru Gong 2021, 42 (8):  1387-1394.  DOI: 10.1016/S1872-2067(20)63647-6 Abstract ( 121 )   HTML ( 11 )   PDF (946KB) ( 329 )   Supporting Information A comprehensive understanding of the role of the electrocatalyst in photoelectrochemical (PEC) water splitting is central to improving its performance. Herein, taking the Si-based photoanodes (n +p-Si/SiOx/Fe/FeOx/MOOH, M = Fe, Co, Ni) as a model system, we investigate the effect of the transition-metal electrocatalysts on the oxygen evolution reaction (OER). Among the photoanodes with the three different electrocatalysts, the best OER activity, with a low-onset potential of ∼1.01 VRHE, a high photocurrent density of 24.10 mA cm -2 at 1.23 VRHE, and a remarkable saturation photocurrent density of 38.82 mA cm -2, was obtained with the NiOOH overlayer under AM 1.5G simulated sunlight (100 mW cm -2) in 1 M KOH electrolyte. The optimal interfacial engineering for electrocatalysts plays a key role for achieving high performance because it promotes interfacial charge transport, provides a larger number of surface active sites, and results in higher OER activity, compared to other electrocatalysts. This study provides insights into how electrocatalysts function in water-splitting devices to guide future studies of solar energy conversion.

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Selective Se doping of NiFe2O4 on an active NiOOH scaffold for efficient and robust water oxidation Yuan Huang, Jian-Jun Wang, Yang Zou, Li-Wen Jiang, Xiao-Long Liu, Wen-Jie Jiang, Hong Liu, Jin-Song Hu 2021, 42 (8):  1395-1403.  DOI: 10.1016/S1872-2067(20)63739-1 Abstract ( 198 )   HTML ( 20 )   PDF (2584KB) ( 495 )   Supporting Information There remains a challenge in designing electrocatalysts for water oxidation to create highly efficient catalytic sites for the oxygen evolution reaction (OER) while maintaining their robustness at large outputs. Herein, an etching-assisted synthesis approach was developed to integrate highly active NiFe2O4 nanoparticles with a robust and active NiOOH scaffold directly on commercial stainless steel. A precise selenization strategy was then introduced to achieve selective Se doping of NiFe2O4 to further enhance its intrinsic OER activity while maintaining a three-dimensional NiOOH nanosheet array as a robust scaffold for prompt mass transfer and gas evolution. The resulting NiFe2O4‒xSex/NiOOH electrode exhibited superior electrocatalytic activity with low overpotentials of 153 and 259 mV to deliver benchmark current densities of 10 and 500 mA cm -2, respectively. More importantly, the catalyst exhibited remarkable durability at a stable current output of 100 mA cm -2 for hundreds of hours. These findings may open up opportunities for exploring efficient and robust electrocatalysts for scalable hydrogen production with practical materials.

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Redox chemistry of N4-Fe 2+ in iron phthalocyanines for oxygen reduction reaction Anuj Kumar, Ying Zhang, Yin Jia, Wen Liu, Xiaoming Sun 2021, 42 (8):  1404-1412.  DOI: 10.1016/S1872-2067(20)63731-7 Abstract ( 139 )   HTML ( 16 )   PDF (1195KB) ( 414 )   Supporting Information A precise understanding of the redox chemistry of Nm-M n+ (like N4-Fe 2+) systems is essential for fundamental studies and rational design of Nm-M n+-based electrocatalysts for the oxygen reduction reaction (ORR). Herein, three different iron phthalocyanines (FePcs) adsorbed on carbon nanotubes ((NH2)4FePc@CNTs, (t-Bu)4FePc@CNTs, and FePc@CNTs) were evaluated to demonstrate the effect of the electron donating power of the substituents on the Fe 3+/Fe 2+redox potential of FePc@CNTs and the role of these composites as ORR mediators in alkaline media. The Fe 3+/Fe 2+redox potential of the FePcs was found to shift towards the cathodic region upon substitution with electron-donating groups. This up-field shift in the eg-orbital leads to a lower overlap between the onset potential of the Fe 3+/Fe 2+ redox couple and that of the ORR, and thus, the ORR activity decreased in the following order based on the substitution of FePc: ‒H > ‒t-Bu > ‒NH2.