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Acidic CO2-to-HCOOH electrolysis represents a sustainable route for value-added CO2 transformations. However, competing hydrogen evolution reaction (HER) in acid remains a great challenge for selective CO2-to-HCOOH production, especially in industrial-level current densities. Main group metal sulfides derived S-doped metals have demonstrated enhanced CO2-to-HCOOH selectivity in alkaline and neutral media by suppressing HER and tuning CO2 reduction intermediates. Yet stabilizing these derived sulfur dopants on metal surfaces at large reductive potentials for industrial-level HCOOH production is still challenging in acidic medium. Herein, we report a phase-engineered tin sulfide pre-catalyst (π-SnS) with uniform rhombic dodecahedron structure that can derive metallic Sn catalyst with stabilized sulfur dopants for selective acidic CO2-to-HCOOH electrolysis at industrial-level current densities. In situ characterizations and theoretical calculations reveal the π-SnS has stronger intrinsic Sn-S binding strength than the conventional phase, facilitating the stabilization of residual sulfur species in the Sn subsurface. These dopants effectively modulate the CO2RR intermediates coverage in acidic medium by enhancing *OCHO intermediate adsorption and weakening *H binding. As a result, the derived catalyst (Sn(S)-H) demonstrates significantly high Faradaic efficiency (92.15 %) and carbon efficiency (36.43 %) to HCOOH at industrial current densities (up to −1 A cm−2) in acidic medium. Stabilizing sulfur dopants on metal surfaces is important but challenging in acidic CO2 to HCOOH electrolysis, especially under high current densities. Here the authors present phase engineered SnS pre-catalyst with stronger intrinsic Sn-S binding strength for CO2 conversion to HCOOH at > 1 A cm−2 in acidic medium. [ABSTRACT FROM AUTHOR]

Vacancy engineering is an effective strategy to manipulate the electronic structure of electrocatalysts to improve their performance, but few reports focus on phosphorus vacancies (Pv). Herein, the creation of Pv in metal phosphides and investigation of their role in alkaline electrocatalytic hydrogen evolution reaction (HER) is presented. The Pv‐modified catalyst requires a minimum onset potential of 0 mV vs. RHE, a small overpotential of 27.7 mV to achieve 10 mA cm−2 geometric current density and a Tafel slope of 30.88 mV dec−1, even outperforms the Pt/C benchmark (32.7 mV@10 mA cm−2 and 30.90 mV dec−1). This catalyst also displays superior stability up to 504 hours without any decay. Experimental analysis and density functional theory calculations suggest Pv can weaken the hybridization of Ni 3d and P 2p orbitals, enrich the electron density of Ni and P atoms nearby Pv, and facilitate H* desorption process, contributing to outstanding HER activity and facile kinetics. [ABSTRACT FROM AUTHOR]

[Display omitted] We demonstrated an efficient solar photovoltaic-powered electrochemical CO 2 reduction device with a high-pressure CO 2 -captured liquid feed. In an "air-to-barrel" picture, this device holds promise to avoid both high-temperature gaseous CO 2 regeneration and high energy-cost gas product separation steps, while these steps are necessary for devices with a gaseous CO 2 feed. To date, solar fuel production with a CO 2 -saturated liquid feed suffers from high over-potential to suppress the hydrogen evolution reaction and consequently, low solar-to-chemical (STC) energy conversion efficiency. Here, we presented a distinct high-pressure operando strategy, i.e., we took extra advantage of the high pressure in catalyst synthesis besides in the period of the CO 2 reduction reaction (CO 2 RR). The power of this strategy was demonstrated by a proof-of-concept device in which a representative copper catalyst was first synthesized in operando in a high-pressure (50 bar) CO 2 -saturated KHCO 3 solution, and then this high-pressure CO 2 -captured liquid was converted to solar fuel using the operando synthesized Cu catalyst. This Cu catalyst achieved 95% CO 2 RR selectivity at the recorded low potential of −0.3 V vs. RHE enabled by the combination of operando facet engineering and oxide derivation. Furthermore, this device achieved a record-high STC efficiency of 21.6% under outdoor illumination, superior to other CO 2 -saturated liquid-fed devices, and compared favorably to gaseous CO 2 -fed devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • High- and low-entropy metal–organic frameworks (MOF) have been demonstrated for hydrogen and oxygen evolution reaction. • These entropy-directed catalysts demonstrates excellent performances for overall water splitting. • A photovoltaic-tandem water splitting system has been assembled with high solar-to-hydrogen energy efficiency. We report a water splitting system based on flow-type electrolytic cells, which are catalyzed by the catalysts composed of anodic high-entropy metal–organic framework (MOF) and cathodic low-entropy nickel, iron-MOF. These MOF catalysts have shown excellent activities for overall water splitting characteristic of small applied voltage (1.64 V at 10 mA cm−2) and strong durability for 100 hrs. Based on these catalysts, a tandem system has been assembled by connecting several flow-type water-splitting cells in series, which require 3.3 V for two cells and 5.32 V for three cells to reach 10 mA cm−2. Further, a solar-to-hydrogen production system has been demonstrated by coupling the tandem water splitting cells with photovoltaic panels, which show high Faradaic efficiencies (98.93 %, 98.95 %, and 98.40 %) and energy efficiencies (18.80 %, 18.80 % and 18.70 %) for single-, two-, and three-cells, respectively. The present work would provide new insights into the design of efficient energy-conversion systems for many applications. [ABSTRACT FROM AUTHOR]

MOFs attracted considerable attention as morphology templates and constitution precursors for synthesis of multiple functional nanocomposites due to their diverse and robust framework structure. In this work, a nickel-phosphide@carbon (Ni 2 P@C) composite with unique nanorod array morphology was synthesized via a facile phosphorization process using Ni(II)-zeolitic imidazolate framework-67 (ZIF-67-Ni) as the precursor. And the effect of phosphorization temperature on the morphology and structure of the products were carefully investigated. The products obtained under different phosphorization temperature were utilized as electrocatalysts for hydrogen evolution reaction (HER). The results showed that Ni 2 P@C nanorod array achieved under the phosphorization temperature of 400 °C demonstrated the highest electrocatalytic activity toward HER in 0.5 M sulfuric acid solution with a low overpotential of 186 mV at the current density of 10 mA cm −2 . Also, high catalytic durability and chemical stability of the Ni 2 P@C nanorod array for HER were achieved. Combing the morphology and structure characterization experiments, the reason for high HER performance of Ni 2 P@C nanorod array obtained at the phosphorization temperature of 400 °C was discussed. This work provides a new guidance for the synthesis of high-performance MOFs-derived electrocatalyst for electrochemical HER. [ABSTRACT FROM AUTHOR]

[Display omitted] • A low crystallinity In-doping MnCo 2 O 4 electrode was prepared by a facile method. • Jahn-Teller distortions of Mn3+ and Co3+ cations in the In/MnCo 2 O 4 were suppressed. • In/MnCo 2 O 4 -NF electrode shows significantly enhanced electrochemical activity. • DFT calculations reveal the impact of In doping in the In/MnCo 2 O 4. Jahn-Teller distortion in the transition metal oxides (TMOs) could cause the poor activity and stability in the potentially promising materials for the supercapacitor and electrocatalyst. Herein, a novel strategy to address this problem by a charge regulation engineering is provided, in which, the Jahn-Teller distortion in the low crystallinity In-doped MnCo 2 O 4 (In/MnCo 2 O 4) in-situ grown on the Nickel foam (NF) (In/MnCo 2 O 4 -NF) by a simple laser-assisted method is significantly reduced. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectrum (XANES) analyses show that the strong electronic interaction between the doped In and Mn/Co suppresses Jahn-Teller distortion of Mn3+ and Co3+ cations in the In/MnCo 2 O 4. Moreover, density functional theory (DFT) calculations reveal that the enhanced electrochemical activity and the effects of suppressed Jahn-Teller distortion. As a result, In/MnCo 2 O 4 -NF material shows a highly supercapacitive performance with a high specific capacitance of 1436.8F g−1 at a current density of 1 A g−1, a high rate capability of 71.9% of the capacitance retention at 20 A g−1, and a superior cycle stability (90.1% of the specific capacitance retention after 16,000 cycles). When being paired with activated carbon, the quasi-solid-state asymmetric supercapacitor provides a maximum energy density of 61.5 Wh kg−1 at a power density of 963.2 W kg−1 and an ultra-long cycling lifespan (84.6% retention after 120,000 cycles at 10 A g−1). Furthermore, In/MnCo 2 O 4 -NF as an electrocatalyst has a high hydrogen evolution reaction (HER) performance with a low overpotential (61.8 mV) and a small Tafel slope (76 mV dec-1). [ABSTRACT FROM AUTHOR]

In this work, we firstly predict through density function theory (DFT) that plasma-regulated 2D high entropy materials can show optimized hydrogen adsorption free energy (ΔG H) for promoting hydrogen evolution reaction (HER). Consequently, 2D high entropy FeNiCoMnVO x oxide arrays are fabricated, and further treated by Ar plasma to generate oxygen vacancies on the surface of catalyst, which possess a well-defined crystal structure that are analogous to the structures of Mn 3 O 4 and the morphology like a number of vertically aligned nanosheets. Remarkably, the catalyst exhibits superior electrocatalytic HER activity with a small overpotential of 81 mV to achieve the current density of 10 mA cm−2 and a Tafel slope of 88 mV dec−1. It can stably operate at 10 mA cm−2 up to 100 h with negligible activity decay. Further combination of experimental results and DFT computations illustrate the synergistic effect of five metal active sites that can dwindle the Gibbs energy barrier of the H* desorption step during the process of HER. In addition, oxygen vacancies which generated by Ar plasma can modulate the surface of catalyst to enrich the electron density of metal sites and contribute superior HER performance. [Display omitted] • DFT calculations predict that plasma-regulated 2D high entropy materials can show optimized ΔG H for promoting HER. • A facile method to prepare 2D defected high entropy materials for electrocatalytic applications. • The synergistic effect of five metal active sites that can reduce the Gibbs energy barrier of H* desorption step. • Oxygen vacancies can enrich the electron density of metal sites, creating more active defect sites for HER. [ABSTRACT FROM AUTHOR]

This work reports a universal dissolution-recrystallization method to synthesize two-dimensional (2D) conductive metal-organic framework (MOF) arrays. The MOF arrays have exhibited excellent structural characteristics for electrochemical reactions, including ultrathin architecture, metallic conductivity, and hierarchical macro-/micro-porosity. Particularly, 2D nickel, iron-MOF arrays act as bifunctional electrocatalysts for water splitting, which deliver a current density of 500 mA cm−2 at an overpotential of 305 mV for anodic oxygen evolution reaction (OER), 359 mV for hydrogen evolution reaction (HER), and ~640 mV for overall reactions. The electrode also shows prolonged stability against bulk water splitting (up to 20 h at 500 mA cm−2). In addition, the water splitting system has been further coupled with commercial solar cells to simulate natural water photolysis, demonstrating a high solar-to-hydrogen efficiency of 17.69%. Mechanism study thorough density function theory (DFT) computations shows strong synergistic effect between Ni and Fe active sites that can reduce the Gibbs energy barrier of hydroxyl dissociation step (OH* → O*) during OER and H* desorption step during HER simultaneously. These promising results open up enormous opportunities of designing versatile low-dimensional conductive MOF architectures for renewable energy applications. [Display omitted] • A general method is reported for synthesizing metallic 2D MOF array. • The material has demonstrated excellent structural advantages for electrocatalysis. • The electrode has shown excellent activities for OER, HER and water splitting. • The solar-to-hydrogen efficiency of the system is as high as 17.69%. • DFT calculations reveal the strong synergistic effect inside the material. [ABSTRACT FROM AUTHOR]