Closing both the carbon and nitrogen loops is a critical venture to support the establishment of the circular, net‐zero carbon economy. Although single atom catalysts (SACs) have gained interest for the electrochemical reduction reactions of both carbon dioxide (CO2RR) and nitrate (NO3RR), the structure–activity relationship for Cu SAC coordination for these reactions remains unclear and should be explored such that a fundamental understanding is developed. To this end, the role of the Cu coordination structure is investigated in dictating the activity and selectivity for the CO2RR and NO3RR. In agreement with the density functional theory calculations, it is revealed that Cu‐N4 sites exhibit higher intrinsic activity toward the CO2RR, whilst both Cu‐N4 and Cu‐N4−x‐Cx sites are active toward the NO3RR. Leveraging these findings, CO2RR and NO3RR are coupled for the formation of urea on Cu SACs, revealing the importance of *COOH binding as a critical parameter determining the catalytic activity for urea production. To the best of the authors’ knowledge, this is the first report employing SACs for electrochemical urea synthesis from CO2RR and NO3RR, which achieves a Faradaic efficiency of 28% for urea production with a current density of −27 mA cm–2 at −0.9 V versus the reversible hydrogen electrode.

Oxide-derived Cu catalysts from Cu 2 O microcrystals are capable of electrochemically converting CO 2 into various value-added chemicals. However, their structural transformation and associated preferred products remain unclear, requiring further investigation. Herein, Cu 2 O microcrystals with controllable low-and high-index facets exposure are fabricated to differentiate the effects of initial exposed facets on their structural reconstruction and product selectivity in electrochemical CO 2 reduction reaction. Combined in situ characterizations and theoretical investigation reveal the direct correlations of Cu 2 O reconstruction and product selectivity to its initial facet exposure. The Cu 2 O low-index facet, being more stable with a high energy barrier on material reduction, tends to partially maintain its original crystalline structure and larger Cu 2 O particle size throughout the transformation. The derived flatter surface and limited Cu 2 O/ Cu interfaces result in a favorable selectivity toward 2-electron transfer products. The chemically active Cu 2 O high-index facet (311) is energetically favorable to be reduced owing to the feasible protonation process, thus experiencing a drastic reconstruction with rich newly formed Cu nanoparticles and evolved fine Cu 2 O grains; Such a reconstruction creates uncoordinated Cu species and abundant boundaries, benefiting charge transfer and increasing the local pH by confining OH − , thus leading to a high selectivity toward C 2+ products.

Green hydrogen represents a critical underpinning technology for achieving carbon neutrality. Although researchers often fixate on its energy inputs, a truly ‘green’ hydrogen production process would also be sustainable in terms of water and materials inputs. To address this holistic challenge, we demonstrate a new green hydrogen production system which can utilize secondary wastewater as the input (preserving scarce fresh water supplies for drinking and sanitation). The enabling feature of the proposed system is a self‐grown bifunctional CoNi electrode which consists of ultrathin, spontaneously deposited CoNi nanosheets on a three‐dimensional nickel foam. As such, a green synthesis process was developed using an immersion procedure at room‐temperature with zero net energy input. Testing revealed that the synthesized CoNi electrodes can reach a current density of 10 mA cm−2 at a small overpotential of 197 mV for the hydrogen evolution reaction and 315 mV for the oxygen evolution reaction in alkalified wastewater. The values are ~16.5% and ~6.5% smaller than that from precious catalysts (20 wt% Pt/C and RuO2, respectively). Importantly, this CoNi catalyst offers outstanding durability for overall wastewater splitting. A prototype solar‐energy‐powered rooftop wastewater splitting system was constructed and can produce more than 100 L hydrogen on a sunny day in Sydney, Australia. Taken together, these results indicate that it is promising to unlock holistically green routes for hydrogen production by wastewater uplifting with regards to water, energy, and materials synthesis.

CO2 reduction, two‐electron O2 reduction, and N2 reduction are sustainable technologies to valorise common molecules. Their further development requires working electrode design to promote the multistep electrochemical processes from gas reactants to value‐added products at the device level. This review proposes critical features of a desirable electrode based on the fundamental electrochemical processes and the development of scalable devices. A detailed discussion is made to approach such a desirable electrode, addressing the recent progress on critical electrode components, assembly strategies, and reaction interface engineering. Further, we highlight the electrode design tailored to reaction properties (e.g., its thermodynamics and kinetics) for performance optimisation. Finally, the opportunities and remaining challenges are presented, providing a framework for rational electrode design to push these gas reduction reactions towards an improved technology readiness level (TRL).