Unveiling the Promotion of Surface‐Adsorbed Chalcogenate on the Electrocatalytic Oxygen Evolution Reaction

Selenite-Decorated Polycrystalline NiO Nanosheets Generated from Cathodic Reconstruction for Electrocatalytic Hydrogen Production

Precatalyst reconstruction in alkaline hydrogen evolution reaction (HER) usually leads to changes in the morphology, composition, and structure, thus improving the catalytic activity, which recently receives intensive attention. However, the design strategies of cathodic reconstruction and the structural features of reconstruction products have not achieved a profound understanding. Here, from the point of thermodynamic stability, metastable nickel selenite dihydrate (NiSeO₃·2H₂O) is deliberately fabricated as a precatalyst to comprehensively study the reconstruction dynamics in alkaline HER. Multiple in/ex situ techniques capture the geometric, component, and phase evolutions, proving that NiSeO₃·2H₂O can be transformed into SeO₃^2--decorated polycrystalline NiO nanosheets with rich active sites and good conductivity under alkaline HER conditions, which act as a real catalytic active species. Density functional theory calculations demonstrate that the adsorption of SeO₃^2- can further promote the HER activity of NiO due to the optimized free energy of water activation and hydrogen adsorption. As a result, the SeO₃^2--NiO catalyst exhibits a low overpotential at -10 mA cm^-2 (90 mV) and long-term stability (>100 h). This work highlights the targeted design of precatalyst to trigger and utilize cathodic reconstruction and provides an available method for the development of adsorption-modulated efficient electrocatalysts.

Boosting Hydrogen Production via Selective Two-electron Mild Electrochemical Oxidation of Tetrahydroisoquinolines Completely to Dihydroisoquinolines

Different from the previous study that biomass derivatives replace water oxidation for enhancing hydrogen production, we found that mild oxidation was more conductive to cathodic hydrogen production. In this study, maximum Faradaic efficiency (>99 %) and lower energy consumption for hydrogen production was achieved by precisely controlling the two-electron mild electrochemical oxidation of tetrahydroisoquinolines (THIQs) to dihydroisoquinolines (DHIQs) in place of the four-electron deep oxidation to isoquinolines (IQs). Moreover, the high value-added DHIQs were prepared from THIQs with high selectivity (>99 %) at the low potential of 1.36 V. Operando electrochemical Raman and density functional theory proved that the high selectivity was attributed to the regulable active species of NiOOH induced by the interaction of Co and Fe for preferentially breaking C-H bond rather than N-H of THIQs. This novel method provides important insight into efficient biomass-assisted hydrogen production.

Effect of Surface‐Adsorbed and Intercalated (Oxy)anions on the Oxygen Evolution Reaction

As the kinetically demanding oxygen evolution reaction (OER) is crucial for the decarbonization of our society, a wide range of (pre)catalysts with various non‐active‐site elements (e.g., Mo, S, Se, N, P, C, Si…) have been investigated. Thermodynamics dictate that these elements oxidize during industrial operation. The formed oxyanions are water soluble and thus predominantly leach in a reconstruction process. Nevertheless, recently, it was unveiled that these thermodynamically stable (oxy)anions can adsorb on the surface or intercalate in the interlayer space of the active catalyst. There, they tune the electronic properties of the active sites and can interact with the reaction intermediates, changing the OER kinetics and potentially breaking the persisting OER *OH/*OOH scaling relations. Thus, the addition of (oxy)anions to the electrolyte opens a new design dimension for OER catalysis and the herein discussed observations deepen the understanding of the role of anions in the OER.

Surface Activation and Ni-S Stabilization in NiO/NiS2 for Efficient Oxygen Evolution Reaction

Manipulating the active species and improving the structural stabilization of sulfur-containing catalysts during the OER process remain a tremendous challenge. Herein, we constructed NiO/NiS₂ and Fe-NiO/NiS₂ as catalyst models to study the effect of Fe doping. As expected, Fe-NiO/NiS₂ exhibits a low overpotential of 270 mV at 10 mA cm^-2 . The accumulation of hydroxyl groups on the surface of materials after Fe doping can promote the formation of highly active NiOOH at a lower OER potential. Moreover, we investigated the level of corrosion of M-S bonds and compared the stability variation of M-S bonds with Fe at different locations. Interestingly, Fe bonded with S in the bulk as the sacrificial agent can alleviate the oxidation corrosion of partial Ni-S bonds and thus endow Fe-NiO/NiS₂ long-term durability. This work could motivate the community to focus more on resolving the corrosion of sulfur-containing materials.

Sulfate-Enabled Nitrate Synthesis from Nitrogen Electrooxidation on a Rhodium Electrocatalyst

The electrocatalytic nitrogen oxidation reaction (NOR) to generate nitrate is gaining increasing attention as an alternative approach to the conventional industrial manufacture. But, current progress in NOR is limited by the difficulties in activation and conversion of the strong N≡N bond (941 kJ mol^-1 ). Herein, we designed to utilize sulfate to enhance NOR performance over an Rh electrocatalyst. After the addition of sulfate, the inert Rh nanoparticles exhibited superior NOR performance with a nitrate yield of 168.0 μmol g_cat ^-1  h^-1 . The ¹⁵ N isotope-labeling experiment confirmed the produced nitrate from nitrogen electrooxidation. A series of electrochemical in situ characterizations and theoretical calculation unveiled that sulfate promoted nitrogen adsorption and decreased the reaction energy barrier, and in situ formed sulfate radicals reduced the activation energy of the potential-determining step, thus accelerating NOR.

The Critical Role of Additive Sulfate for Stable Alkaline Seawater Oxidation on Nickel-Based Electrodes

Seawater electrolysis to produce hydrogen is a critical technology in marine energy projects; however, the severe anode corrosion caused by the highly concentrated chloride is a key issue should be addressed. In this work, we discover that the addition of sulfate in electrolyte can effectively retard the corrosion of chloride ions to the anode. We take nickel foam as the example and observe that the addition of sulfate can greatly improve the corrosion resistance, resulting in prolonged operating stability. Theoretical simulations and in situ experiments both demonstrate that sulfate anions can be preferentially adsorbed on anode surface to form a negative charge layer, which repulses the chloride ions away from the anode by electrostatic repulsion. The repulsive effect of the adsorbed sulfate is also applicable in highly-active catalyst (nickel iron layered double hydroxide) on nickel foam, which shows ca. 5 times stability of that in traditional electrolyte.

The Role of Surface Curvature in Electrocatalysts

Excessive consumption of fossil fuels has caused unavoidable environmental problems. The development of renewable and clean alternatives is essential for the sustainable and green development of human society. Electrocatalysts are most important parts in these energy-related devices. Recently, scientists found that the surface curvature of electrocatalysts could play an important role for the improvement of catalytic performance and the optimization of intrinsic catalytic activity during electrocatalytic process. The role of surface curvature in electrocatalysts is still under investigating. In this minireview, we summarized the latest progress of electrocatalysts with different surface curvatures and their applications in energy-related applications. This review mainly involves the strategies for preparation of electrocatalysts with different surface curvatures, three typical electrocatalysts with different surface curvatures (curled surface, onion-like structure, and spiral structure), and the potential mechanisms that surface curvature in electrocatalysts affects activities.

Integrating Hydrogen Production and Transfer Hydrogenation with Selenite Promoted Electrooxidation of α-Nitrotoluenes to E-Nitroethenes

Developing an electrochemical carbon-added reaction with accelerated kinetics to replace the low-value and sluggish oxygen evolution reaction (OER) is markedly significant to pure hydrogen production. Regulating the critical steps to precisely design electrode materials to selectively synthesize targeted compounds is highly desirable. Here, inspired by the surfaced adsorbed SeO_x ^2- promoting OER, NiSe is demonstrated to be an efficient anode enabling α-nitrotoluene electrooxidation to E-nitroethene with up to 99 % E selectivity, 89 % Faradaic efficiency, and the reaction rate of 0.25 mmol cm^-2  h^-1 via inhibiting side reactions for energy-saving hydrogen generation. The high performance can be associated with its in situ formed NiOOH surface layer and absorbed SeO_x ^2- via Se leaching-oxidation during electrooxidation, and the preferential adsorption of two -NO₂ groups of intermediate on NiOOH. A self-coupling of α-carbon radicals and subsequent elimination of a nitrite molecule pathway is proposed. Wide substrate scope, scale-up synthesis of E-nitroethene, and paired productions of E-nitroethene and hydrogen or N-protected aminoarenes over a bifunctional NiSe electrode highlight the promising potential. Gold also displays a similar promoting effect for α-nitrotoluene transformation like SeO_x ^2- , rationalizing the strategy of designing materials to suppress side reactions.

Surface-Adsorbed Carboxylate Ligands on Layered Double Hydroxides/Metal-Organic Frameworks Promote the Electrocatalytic Oxygen Evolution Reaction

Metal-organic frameworks (MOFs) with carboxylate ligands as co-catalysts are very efficient for the oxygen evolution reaction (OER). However, the role of local adsorbed carboxylate ligands around the in-situ-transformed metal (oxy)hydroxides during OER is often overlooked. We reveal the extraordinary role and mechanism of surface-adsorbed carboxylate ligands on bi/trimetallic layered double hydroxides (LDHs)/MOFs for OER electrocatalytic activity enhancement. The results of X-ray photoelectron spectroscopy (XPS), synchrotron X-ray absorption spectroscopy, and density functional theory (DFT) calculations show that the carboxylic groups around metal (oxy)hydroxides can efficiently induce interfacial electron redistribution, facilitate an abundant high-valence state of nickel species with a partially distorted octahedral structure, and optimize the d-band center together with the beneficial Gibbs free energy of the intermediate. Furthermore, the results of in situ Raman and FTIR spectra reveal that the surface-adsorbed carboxylate ligands as Lewis base can promote sluggish OER kinetics by accelerating proton transfer and facilitating adsorption, activation, and dissociation of hydroxyl ions (OH^- ).

Rational Construction of a N, F Co-doped Mesoporous Cobalt Phosphate with Rich-Oxygen Vacancies for Oxygen Evolution Reaction and Supercapacitors

Transition-metal phosphates have been widely applied as promising candidates for electrochemical energy storage and conversion. In this study, we report a simple method to prepare a N, F co-doped mesoporous cobalt phosphate with rich-oxygen vacancies by in-situ pyrolysis of a Co-phosphate precursor with NH₄ ⁺ cations and F^- anions. Due to this heteroatom doping, it could achieve a current density of 10 mA/cm² at lower overpotential of 276 mV and smaller Tafel slope of 57.11 mV dec^-1 on glassy carbon. Moreover, it could keep 92 % of initial current density for 35 h, indicating it has an excellent stability and durability. Furthermore, the optimal material applied in supercapacitor displays specific capacitance of 206.3 F g^-1 at 1 A ⋅ g^-1 and maintains cycling stability with 80 % after 3000 cycles. The excellent electrochemical properties should be attributed to N, F co-doping into this Co-based phosphate, which effectively modulates its electronic structure. In addition, its amorphous structure provides more active sites; moreover, its mesoporous structure should be beneficial to mass transfer and electrolyte diffusion.

Trimetallic Spinel NiCo2-x Fex O4 Nanoboxes for Highly Efficient Electrocatalytic Oxygen Evolution

The development of efficient and low-cost electrocatalysts toward the oxygen evolution reaction (OER) is critical for improving the efficiency of several electrochemical energy conversion and storage devices. Here, we report an elaborate design and synthesis of porous Co-based trimetallic spinel oxide nanoboxes (NiCo_2-x Fe_x O₄ NBs) by a novel metal-organic framework engaged strategy, which involves chemical etching, cation exchange, and subsequent thermal oxidation processes. Owing to the structural and compositional advantages, the optimized trimetallic NiCo_2-x Fe_x O₄ NBs (x is about 0.117) deliver superior electrocatalytic performance for OER with an overpotential of 274 mV at 10 mA cm^-2 , a small Tafel slope of 42 mV dec^-1 , and good stability in alkaline electrolyte, which is much better than that of Co-based bi/monometallic spinel oxides and even commercial RuO₂ .

A Glass-Ceramic with Accelerated Surface Reconstruction toward the Efficient Oxygen Evolution Reaction

The effective non-precious metal catalysts toward the oxygen evolution reaction (OER) are highly desirable for electrochemical water splitting. Herein, we prepare a novel glass-ceramic (Ni_1.5 Sn@triMPO₄ ) by embedding crystalline Ni_1.5 Sn nanoparticles into amorphous trimetallic phosphate (triMPO₄ ) matrix. This unique crystalline-amorphous nanostructure synergistically accelerates the surface reconstruction to active Ni(Fe)OOH, due to the low vacancy formation energy of Sn in glass-ceramic and high adsorption energy of PO₄ ^3- at the V_O sites. Compared to the control samples, this dual-phase glass-ceramic exhibits a remarkably lowered overpotential and boosted OER kinetics after surface reconstruction, rivaling most of state-of-the-art electrocatalysts. The residual PO₄ ^3- and intrinsic V_O sites induce redistribution of electron states, thus optimizing the adsorption of OH* and OOH* intermediates on metal oxyhydroxides and promoting the OER activity.