Polyarene Oxides with Tunable Quinone Units for Photocatalytic CO2 Reduction: A Simple Strategy toward Effective and Selective Catalysts.

The photocatalytic transformation of carbon dioxide (CO2) into valuable chemicals is a challenging process that requires effective and selective catalysts. However, most polymer-based photocatalysts with electron donor-acceptor (D-A) structures are synthesized with a fixed D-A ratio by using expensive monomers. Herein, we report a simple strategy to prepare polyarene oxides (PAOs) with quinone structural units via oxidation treatment of polyarene (PA). The resultant PAOs show tunable D-A structures and electronic band positions depending on the degree of oxidation, which can catalyze the photoreduction of CO2 with water under visible light irradiation, generating CO as the sole carbonaceous product without H2 generation. Especially, the PAO with an oxygen content of 17.6% afforded the highest CO production rate of 161.9 µmol g-1 h-1. It is verified that the redox transformation between quinone and phenolic hydroxyl in PAOs achieves CO2 photoreduction coupled with water oxidation. This study provides a facile way to access conjugated polymers with a tunable D-A structure and demonstrates that the resultant PAOs are promising photocatalysts for CO2 reduction.

Alkyl sulfonate surfactant mediates electroreduction of carbon dioxide to ethylene or ethanol over hydroxide-derived copper catalysts.

For CO2 electroreduction (CO2ER) to C2 compounds, it is generally accepted that the formation of ethylene and ethanol shares the same intermediate, *HCCOH. The majority of studies have achieved high faradaic efficiency (FE) towards ethylene, but faced challenges to get high ethanol FE. Herein, we present an alkyl sulfonate surfactant (e.g., sodium dodecyl sulfonate, SDS) mediated CO2ER to a C2 product over an in situ generated Cu catalyst (Cu@SDS) from SDS-modified Cu(OH)2. It achieves the CO2ER to ethylene as the sole C2 product at low applied voltages with a FE of 55% at -0.6 V vs. RHE and to ethanol as the main product at potentials ≥0.7 V with a maximum FE of 64% and a total C2 FE of 86% at -0.8 V, with a current density of 231 mA cm-2 in a flow cell. Mechanism investigation indicates that SDS modifies the oxidation state of the in situ formed Cu species in Cu@SDS, thus tuning the catalyst activity for CO2ER and lowering the C-C coupling energy barrier; meanwhile, it tunes the adsorption mode of the *HCCOH intermediates on the catalyst, thus mediating the selectivity of CO2ER towards C2 products.

Ag Single Atoms Anchored on CeO2 with Interfacial Oxygen Vacancies for Efficient CO2 Electroreduction.

Ag single-atom catalysts (SACs) have great potential in selective electrocatalysis of the CO2 reduction reaction (CO2RR) to CO, while it is still a challenge to achieve high current density and high atom efficiency simultaneously. Here, we present a new and simple in situ adsorption-reduction method to prepare Ag SACs supported on CeO2 (Ag1/CeO2). It is found that Ag single atoms are anchored on CeO2 through strong metal-support interaction (SMSI), and each Ag atom is accompanied with three interfacial oxygen vacancies. This Ag1/CeO2 exhibits high performance in the electrocatalytic CO2RR with a high CO faradaic efficiency (FE) of >95% under a wide potential range. The turnover frequency (TOF) value can reach 50,310 h-1 at FECO = 99.5% in H-cells. Notably, Ag1/CeO2 achieves an industrial-grade current density of 403 mA cm-2 with a high FECO of 97.2% in flow cells. Experimental results combined with density functional theory calculation revealed that this superior performance was mainly ascribed to the existence of interfacial oxygen vacancies, which lead to the formation of Ag-O-Ce3+ atomic interfaces, and activates the Ce3+-O structures as the synergistic active center of Ag, thus promoting CO2 adsorption and activation and reducing the reaction potential barrier of *COOH-to-*CO.

Partially Nitrided Ni Nanoclusters Achieve Energy-Efficient Electrocatalytic CO2 Reduction to CO at Ultralow Overpotential.

Electrocatalytic CO2 reduction reaction (CO2 RR) offers a promising strategy to lower CO2 emission while producing value-added chemicals. A great challenge facing CO2 RR is how to improve energy efficiency by reducing overpotentials. Herein, partially nitrided Ni nanoclusters (NiNx ) immobilized on N-doped carbon nanotubes (NCNT) for CO2 RR are reported, which achieves the lowest onset overpotential of 16 mV for CO2 -to-CO and the highest cathode energy efficiency of 86.9% with CO Faraday efficiency >99.0% to date. Interestingly, NiNx /NCNT affords a CO generation rate of 43.0 mol g-1  h-1 at a low potential of -0.572 V (vs RHE). DFT calculations reveal that the NiNx nanoclusters favor *COOH formation with lower Gibbs free energy than isolated Ni single-atom, hence lowering CO2 RR overpotential. As NiNx /NCNT is applied to a membrane electrode assembly system coupled with oxygen evolution reaction, a cell voltage of only 2.13 V is required to reach 100 mA cm-2 , with total energy efficiency of 62.2%.

Interface engineered Co, Ni, Fe, Cu oxide hybrids with biphasic structures for water splitting with enhanced activity.

Developing high-performance catalysts for water splitting via renewable electricity is of great significance for the clean production of hydrogen. This work reports rational design and controllable fabrication of metal oxide hybrid catalyst CoNiFe2O5·2CuO with unique biphasic microstructures for electrochemical water splitting. Benefited from the presence of CuO nanoparticles as the second phase, more defects and active sites were formed around the interfaces of CoNiFe2O5 and CuO, which led to excellent performances for electrocatalytic water splitting. In particular, the catalyst exhibited outstanding activity for hydrogen evolution reaction with a small overpotential of 30 mV to reach a current density of 10 mA cm-2 and showed a higher turnover frequency (0.3 s-1) than commercial catalyst Pt/C (0.1 s-1) under an overpotential of 50 mV. Moreover, it also displayed good activity for oxygen evolution reaction with an overpotential of 264 mV at 10 mA cm-2. Using CoNiFe2O5·2CuO as the catalyst for electrode pair to construct a cell, a very low cell voltage of 1.53 V is enough to achieve overall water splitting at 10 mA cm-2 in 1 M KOH electrolyte, and the cell could maintain the stable performance at 10 mA cm-2 within 100 h. The as-prepared metal oxide hybrids with biphasic microstructures may have promising application potentials in water splitting.

Tuning d-Band Structure of CuII in Coordinated Polymer via d-π Conjugation for Improving CO2 Electroreduction Selectivity toward C2 Products.

Copper-coordinated catalysts are reported to be effective for electrocatalytic CO2 reduction reaction (CO2 RR) to C2 products but suffer from low selectivity. Herein a strategy was developed to tune the d-band structure of CuII via coordinating with aromatic ligands to form Cu-based conjugated polymers for CO2 RR to C2 chemicals. The catalysts derived from copper chloride coordinating with tetraminobenzoquinone (TABQ) and with 1,2,4,5-benzenetetramine possessed high-density and compact Cu single-atom sites and displayed high activity for CO2 RR to C2 products. Especially, Cu-TABQ exhibited a maximum C2 faradaic efficiency of 63.2 % with a current density of 423 mA cm-2 at -1.17 V (vs. reversible hydrogen electrode). Density functional theory calculations indicated that the TABQ linker possessing C=O groups significantly widened the d-band of coordinated CuII , which facilitated binding of *CO intermediate on the catalyst and thus enhanced C-C coupling. This work provides mechanistic insight into the CuII -coordinated polymers for CO2 RR with high selectivity toward C2 products.