The electrochemical conversion of carbon dioxide (CO₂) into valuable chemicals is a feasible way to mitigate the negative impacts of overmuch CO₂ emissions. Porphyrin-based metal organic frameworks (MOFs) are expected to be used for selective and efficient electrochemical CO₂ reduction (ECR) with porous structure and ordered active sites. Herein, we report the synthesis of a monodispersed and spherical organic/inorganic hybrid Cu-TCPP@Cu₂O electrocatalyst composed of Cu-TCPP (TCPP = tetrakis (4-carboxyphenyl) porphyrin) and Cu₂O, where TCPP plays significant roles in regulating the morphology. In-situ formed Cu during ECR process in combination with Cu-TCPP (Cu-TCPP@Cu) can suppress hydrogen evolution, enrich CO intermediate and promote C–C coupling toward C₂ products. The Cu-TCPP@Cu supported on porous carbon (PC) showed ultrafine Cu nanoclusters on PC, and displayed high ECR activity and selectivity toward C₂ products, with a C₂ faradaic efficiency of 62.3% at –1.0 V versus the reversible hydrogen electrode and a C₂ partial current density of 83.4 mA·cm^–2, which is 7.6 times and 13.1 times those of pure Cu₂O and TCPP, respectively. The morphology and hybrid structure of the catalyst were studied to improve the selectivity of ECR to produce C₂ products, which provides a new idea for the design of high-performance ECR catalyst.

Transition metal phosphide (TMP) is a kind of effective catalysts toward hydrogen evolution reaction (HER) in alkaline electrolytes. However, the performance of TMP catalysts is strongly limited by water splitting. In this work, we developed a method to prepare a copper foam (CF) supported Ru-doped Cu₃P catalyst (Ru-Cu₃P/CF) by a consecutive growth of Cu(OH)₂ nanoarrays, soaking in RuCl₃ solution and phosphorization. A large surface area was obtained by the self-supported catalysts with the appropriative Ru doping. As an excellent HER catalyst, it exhibited a low overpotential of 95.6 mV at a current density of 10 mA·cm^-2, which is 149.4 mV lower than that of Cu₃P/CF without Ru-doping. The Tafel slope was reduced from 136.6 to 73.6 mA·dec^-1 and the rate determining step was changed from Volmer step to Heyrovsky step. The improvement of HER performance might be attributed to the facilitated water splitting step by Ru-doping, which provides more active sites for water splitting. The nanoparticles morphology of Ru-Cu₃P derived from the Cu(OH)₂ arrays ensured large electrochemical surface areas of the supported electrodes, which could promote the mass and electron transfers, and promote gas production and bubble release. This work highlights the importance of the tuning of the water splitting step and surface engineering by the transition metal with emptier d orbitals, which may pave the road for design of high-performance HER electrocatalyst.

Electrocatalytic water splitting represents grand promise for hydrogen fuel in modern energy equipment, and the design and fabrication of higher performance catalysts are at the central. Herein, we report the sequential phosphorus (P)-doping into ruthenium (Ru) nanoparticles (Ru-P/C) by thermal annealing of Ru nanoparticles in phosphine (PH₃) atmosphere and deposition of extremely low concentration of platinum (Pt) to obtain P-doped Ru-Pt alloy catalyst supported on carbon nanotubes (CNTs), which is denoted as (Ru-P)#Pt/C. The data by X-ray diffraction spectroscopy and transmission electron microscopy show that the Ru nanoparticles existed in the form of hexagonal close-packed (hcp) phase with low crystallinity. The results by high-resolution X-ray photoelectron spectroscopy indicate that Ru was mainly in metallic state, and Pt was slightly and positively charged, ascribing to the bonding with P atoms. This indicates that the highly diluted Pt atoms may be dispersed on the surface of Ru nanoparticles through Ru-P-Pt bonds. Accordingly, the as-prepared (Ru-P)#Pt/C alloy catalysts displayed excellent alkaline hydrogen evolution activity, revealing only 17 mV vs. RHE at a current density of 10 mA·cm^–2 and a Tafel slope value of 27 mV·dec^–1, superior to those of the controlled samples Ru-P/C and trace amount of Pt loaded P-doped CNTs (Pt/C-P). Density functional theory (DFT) calculation suggests that P-doping into Ru can enhance the adsorption of water molecules and the activation for water splitting, while the Pt site on Ru-Pt alloy can behave as the hydrogen desorption site. Thus, the superior performance of (Ru-P)#Pt/C alloy catalyst might be attributed to the synergistic effect of P-doped Ru sites and Pt sites, which significantly improves the alkaline hydrogen evolution reaction kinetics.

The catalytic activity of the catalysts is strongly dependent on the structure of the catalysts, and the exploration of their correlation and structure-controlled synthesis of the high-performance catalysts are always at the central. Currently, platinum (Pt) is the optimum catalyst for hydrogen evolution reaction (HER), oxygen reduction reaction (ORR) and alcohol oxidation reaction, while ruthenium (Ru) behaves as the champion catalyst for oxygen evolution reaction (OER) during water splitting. Preparing alloy catalysts with these precious metals can modulate the catalytic activity of these catalysts from the perspective of strain effect, ensemble effect and ligand effect. Here, we developed a strategy to deposit AuPt alloy as a solid solution phase on amorphous Ru supported on CNTs, thus forming AuPt-Ru heterostructures. The well-defined AuPt-Ru heterostructured catalysts were examined by X-ray diffraction and elemental mapping in high-angle annular dark-field scanning transition electron spectroscopy (HAADF-STEM). As compared to the high crystallinity AuPt alloy, AuPt alloy in AuPt-Ru heterostructure became amorphous, and AuPt-Ru showed superior catalytic activity toward ethanol oxidation reaction (EOR), achieving the mass activity of Pt as high as 21.44 A·mg^-1 due to the high tolerance toward the poisoning species. The intermediates species of the EOR were also examined by in-situ FTIR spectroscopy. The stability of the catalysts toward EOR was also excellent and the degradation in the activity of the catalysts was strongly related to the loss of Ru content during the stability test. The heterostructured AuPt-Ru catalysts also exhibited the excellent alkaline HER and OER performances, superior to those of commercial Pt/C and RuO₂ catalysts, ascribing to the amorphous state of AuPt-Ru heterostructure, and the modulation by strain and ensemble effects. This work highlights the importance in the design of the multicomponent heterostructures for the synthesis of high-performance and multifunctional electrocatalysts.