Unraveling the Synergy of Anion Modulation on Co Electrocatalysts by Pulsed Laser for Water Splitting: Intermediate Capturing by In Situ/Operando Raman Studies.

Herein, the authors produce Co-based (Co3 (PO4 )2 , Co3 O4 , and Co9 S8 ) electrocatalysts via pulsed laser ablation in liquid (PLAL) to explore the synergy of anion modulation on phase-selective active sites in the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Co3 (PO4 )2 displays an ultralow overpotential of 230 mV at 10 mA cm-2 with 48.5 mV dec-1 Tafel slope that outperforms the state-of-the-art Ir/C in OER due to its high intrinsic activity. Meanwhile, Co9 S8 exhibits the highest HER performance known to the authors among the synthesized Co-based catalysts, showing the lowest overpotential of 361 mV at 10 mA cm-2 with 95.8 mV dec-1 Tafel slope in the alkaline medium and producing H2 gas with ≈500 mmol g-1 h-1 yield rate under -0.45 V versus RHE. The identified surface reactive intermediates over in situ electrochemical-Raman spectroscopy reveal that cobalt(hydr)oxides with higher oxidation states of Co-cation forming under oxidizing potentials on the electrode-electrolyte surface of Co3 (PO4 )2 facilitate the OER, while Co(OH)2 facilitate the HER. Notably, the fabricated two-electrode electrolyzers using Co3 (PO4 )2 , Co3 O4 , and Co9 S8 electrocatalysts deliver the cell potentials ≈2.01, 2.11, and 1.89 V, respectively, at 10 mA cm-2 . This work not only shows PLAL-synthesized electrocatalysts as promising candidates for water splitting, but also provides an underlying principle for advanced energy-conversion catalysts and beyond.

Anion Modulation of Pt-Group Metals and Electrocatalysis Applications.

Pt-group metal (PGM) electrocatalysts with unique electronic structures and irreplaceable comprehensive properties play crucial roles in electrocatalysis. Anion engineering can create a series of PGM compounds (such as RuP2 , IrP2 , PtP2 , RuB2 , Ru2 B3 , RuS2 , etc.) that provide a promising prospect for improving the electrocatalytic performance and use of Pt-group noble metals. This review seeks the electrochemical activity origin of anion-modulated PGM compounds, and systematically analyzes and summarizes their synthetic strategies and energy-relevant applications in electrocatalysis. Orientation towards the sustainable development of nonfossil resources has stimulated a blossoming interest in the design of advanced electrocatalysts for clean energy conversion. The anion-modulated strategy for Pt-group metals (PGMs) by means of anion engineering possesses high flexibility to regulate the electronic structure, providing a promising prospect for constructing electrocatalysts with superior activity and stability to satisfy a future green electrochemical energy conversion system. Based on the previous work of our group and others, this review summarizes the up-to-date progress on anion-modulated PGM compounds (such as RuP2 , IrP2 , PtP2 , RuB2 , Ru2 B3 , RuS2 , etc.) in energy-related electrocatalysis from the origin of their activity and synthetic strategies to electrochemical applications including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), N2 reduction reaction (NRR), and CO2 reduction reaction (CO2 RR). At the end, the key problems, countermeasures and future development orientations of anion-modulated PGM compounds toward electrocatalytic applications are proposed.

Progress in Manipulating Dynamic Surface Reconstruction via Anion Modulation for Electrocatalytic Water Oxidation.

The development of efficient and economical electrocatalysts for oxygen evolution reaction (OER) is of paramount importance for the sustainable production of renewable fuels and energy storage systems; however, the sluggish OER kinetics involving multistep four proton-coupled electron transfer hampers progress in these systems. Fortunately, surface reconstruction offers promising potential to improve OER catalyst design. Anion modulation plays a crucial role in controlling the extent of surface reconstruction and positively persuading the reconstructed species' performances. This review starts by providing a general explanation of how various types of anions can trigger dynamic surface reconstruction and create different combinations with pre-catalysts. Next, the influences of anion modulation on manipulating the surface dynamic reconstruction process are discussed based on the in situ advanced characterization techniques. Furthermore, various effects of survived anionic groups in reconstructed species on water oxidation activity are further discussed. Finally, the challenges and prospects for the future development directions of anion modulation for redirecting dynamic surface reconstruction to construct highly efficient and practical catalysts for water oxidation are proposed.

Anion-Incorporated Mg-Ion Solvation Modulation Enables Fast Magnesium Storage Kinetics of Conversion-Type Cathode Materials.

Rechargeable magnesium batteries (RMB) have emerged as one of the most promising alternatives to lithium-ion batteries due to the prominent advantages of magnesium metal anodes. Nevertheless, their application is hindered by sluggish Mg-ion storage kinetics in cathodes, although various structural modifications of cathode materials have been performed. Herein, an electrolyte design using an anion-incorporated Mg-ion solvation structure is developed to promote the Mg-ion storage reactions of conversion-type cathode materials. The addition of the trifluoromethanesulfonate anion (OTf- ) in the ether-based Mg-ion electrolyte modulates the solvation structure of Mg2+ from [Mg(DME)3 ]2+ to [Mg(DME)2.5 OTf]+ (DME = dimethoxy ethane), which facilitates Mg-ion desolvation and thus significantly expedites the charge transfer of the cathode material. As a result, the as-prepared CuSe cathode material on copper current collector exhibits a considerable increase in magnesium storage capacity from 61% (228 mAh g-1 ) to 95% (357 mAh g-1 ) of the theoretical capacity at 0.1 A g-1 and a more than twofold capacity increase at a high current density of 1.0 A g-1 . This work provides an efficient strategy via electrolyte modulation to achieve high-rate conversion-type cathode materials for RMBs. The incorporation of the trifluoromethanesulfonate anion in the Mg-ion solvation structure of the borate-based Mg-ion electrolyte enables the fast magnesium storage kinetics of the conversion-type cathode materials. The as-prepared copper selenide cathode achieved a more than twofold capacity increase at a high rate and the highest reversible capacities compared to those of the previously reported metal selenide cathodes.

Boosting Ammonia Uptake within Metal-Organic Frameworks by Anion Modulating Strategy.

Ammonia with toxic and corrosive features needs advanced protective materials and removal tools, although it is a vital component in human food supply processes. So, to satisfy these requirements, materials with high adsorption capacity and affinity for ammonia should be developed. The present research has been focused on a series zinc-based metal-organic frameworks (MOF) containing mixed ligands, biphenyl dicarboxylic acid (BPDA) and tris(4-(4H-1,2,4-triazol-4-yl)phenyl)amine (TTPA), which are modulated by different anions including CH3COO-, CF3COO-, and CF3SO3-. Ammonia uptake capacity was measured via static and dynamic conditions under 50% relative humidity. Among all compounds, CF3SO3- anion could enhance the ammonia uptake capacity of MOFs up to 177.85 and 349 mg/g during static and breakthrough measurements, respectively, so that 83.30% of the total uptake capacity (at P/Po = 1.0 and 298 K) was achieved at low relative pressure range (up to 0.1). The isosteric heats of ammonia adsorption on PFC-27 and derivatives were calculated in the range of 7.03-10.16 kJ mol-1 so that they increased upon CF3SO3-, CF3COO-, and CH3COO- ion incorporation. This is potentially beneficial for enhanced ammonia adsorption. Interestingly, adsorption capacities were retained with only slight changes after five cycles and three regeneration temperatures, 25 °C, 60 °C, and 120 °C, under vacuum. The special affinity for NH3 adsorption and MOF phase stability after desorption is clearly proved by FTIR spectra and PXRD analysis, respectively. Generally, the results suggest that ion insertion modification is an efficient strategy for enhancement of MOF adsorption performance.

Highly Crystalline Hollow Toroidal Copper Phosphosulfide via Anion Exchange: A Versatile Cation Exchange Nanoplatform.

Postmodification of nanocrystals through cation exchange has been very successful in diversifying nanomaterial compositions while retaining the structural motif. Copper compound nanoparticles are particularly useful as templates because of inherent defects serving as effective cation diffusion routes and excellent cation mobility. Therefore, the development of shape-controlled multianion systems, such as copper phosphosulfide, can potentially lead to the formation of diverse metal phosphosulfide nanomaterials that have otherwise inaccessible compositions and structures. However, there is, to the best of our knowledge, no report on the shape-controlled synthesis of copper phosphosulfide nanoparticles because the introduction of the second anion to the metal compound might destroy the nanoparticle morphology and crystallinity due to the required high energy for anion diffusion and mixing. Herein, we report that it is feasible to transfer the structural motif of copper sulfide to copper phosphosulfide using tris(diethylamino)phosphine. The anion-mixed copper phosphosulfide in the form of a hollow toroid could provide a pathway to previously inaccessible phases and morphologies. We verified the versatility of a copper phosphosulfide hollow toroid as a cation-exchange template by the successful synthesis of cobalt, nickel, indium, and cadmium phosphosulfides as well as bimetallic cobalt-nickel phosphosulfide (Co2-xNixP1-ySy) with a retained structural motif.