TCO2 contracts

TCO2 tokens represents tokenized carbon credits

A separate TCO2 contract is created for each different vintage issuance. Each token contract has the same standard functions, extends ERC20, and is upgradeable.

Find out more about how we name TCO2s in the Carbon Rosetta Stone.

Currently, we support TCO2s for two different carbon registries, Puro and Verra, each with a varying degree of functionality documented below.

getAttributes

Function to get corresponding attributes from the carbon project vintage that is represented by this TCO2 contract.

function getAttributes() public view virtual returns (ProjectData memory, VintageData memory);

The return values are tuples — below you can find the definitions of the ProjectData & VintageData structs.

struct ProjectData {
    string projectId;
    string standard;
    string methodology;
    string region;
    string storageMethod;
    string method;
    string emissionType;
    string category;
    string uri;
    address beneficiary;
}

struct VintageData {
    /// @dev A human-readable string which differentiates this from other vintages in
    /// the same project, and helps build the corresponding TCO2 name and symbol.
    string name; // the vintage year
    uint64 startTime; // UNIX timestamp
    uint64 endTime; // UNIX timestamp
    uint256 projectTokenId;
    uint64 totalVintageQuantity;
    bool isCorsiaCompliant;
    bool isCCPcompliant;
    string coBenefits;
    string correspAdjustment;
    string additionalCertification;
    string uri;
    string registry;
}

Puro

The integration with Puro is achieved through a two-way bridge, where state is synced between the registry and onchain. For more high-level info on the Puro bridge read here.

To ensure a robust sync between the Puro offchain registry and the Toucan onchain contracts, our Puro TCO2 contracts use an escrow contract to hold TCO2s temporarily. The TCO2s are escrowed on every detokenization or retirement request, until the request is completed in the registry, before it can be finalized onchain.

Developers only need to care about creating the request with one of the functions documented below, then it's up to Toucan to finalize the request. In the future, we envision deprecating the admin functionality to process requests offchain and finalize onchain with the use of oracles.

requestDetokenization

function requestDetokenization(uint256[] tokenIds, uint256 amount) external returns (uint256 requestId)

Request a detokenization of batch-NFTs. The amount of TCO2 to detokenize will be transferred from the user to an escrow contract. The detokenization request will be processed asynchronously by Toucan so callers should monitor the status of the request by listening to the DetokenizationFinalized and DetokenizationReverted events.

This function is permissionless and can be called by anyone with enough TCO2 to detokenize

Parameters

Name	Type	Description
tokenIds	uint256[]	Token IDs of one or more batches to detokenize
amount	uint256	The amount of TCO2 to detokenize, must be greater than zero and equal to or smaller than the total amount of the batches (and also greater then the total amount of all the batches except the last one)

Return Values

Name	Type	Description
requestId	uint256	The ID of the request in the escrow contract

requestRetirement

function requestRetirement(struct CreateRetirementRequestParams params) external returns (uint256 requestId)

Request a retirement of TCO2s from batch-NFTs. The amount of TCO2s to retire will be transferred from the user to an escrow contract. The retirement request will be processed asynchronously by Toucan so callers should monitor the status of the request by listening to the RetirementFinalized and RetirementReverted events.

This function is permissionless and can be called by anyone with enough TCO2 to retire

Parameters

Name	Type	Description
params	struct CreateRetirementRequestParams	The parameters of the retirement request:
		- uint256[] tokenIds: One or more batches to retire
		- uint256 amount: The amount of TCO2 to retire; must be greater than zero and equal to or smaller than the total amount of the batches (and also greater than the total amount of all batches except the last one)
		- string retiringEntityString: An identifiable string for the retiring entity, e.g., their name
		- address beneficiary: The address of the beneficiary of the retirement
		- string beneficiaryString: An identifiable string for the beneficiary, e.g., their name
		- string retirementMessage: A message to include in the retirement certificate
		- string beneficiaryLocation: The location of the beneficiary of the retirement
		- string consumptionCountryCode: The country code of the consumption location
		- uint256 consumptionPeriodStart: The start of the consumption period, in seconds since the epoch
		- uint256 consumptionPeriodEnd: The end of the consumption period, in seconds since the epoch

Return Values

Name	Type	Description
requestId	uint256	The ID of the request in the escrow contract

Verra

Note that the Verra bridge does not support bringing new credits onchain anymore. Nevertheless for existing Verra credits, we support direct onchain retirements, which can be executed using any of the functions documented below.

retire

To retire a given amount of CO2 tons. The credits are permanently removed from circulation — this achieves the offset. This also emits a Retired event.

function retire(uint256 amount) public virtual returns (uint256 retirementEventId);

Params

Name	Type	Description
amount	uint256	Amount of TCO2 tokens to retire

Return values

Name	Type	Description
retirementEventId	uint256	The ID of the event emitted upon retirement. Can be used later to mint RetirementCertificates

retireFrom

Achieves similar functionality as retire(), but instead of retiring from the caller's address, it does so from the provided address. This allow for pools or third party contracts to retire for the user.

This function requires the user to approve the third party from the TCO2 contract.

function retireFrom(address account, uint256 amount) external virtual returns (uint256 retirementEventId);

Params

Name	Type	Description
account	address	Address from which to retire
amount	uint256	Amount of TCO2 tokens to retire

Return values

Name	Type	Description
retirementEventId	uint256	The ID of the event emitted upon retirement. Can be used later to mint RetirementCertificates

retireAndMintCertificate

Retires an amount of TCO2 tokensand mints a certificate, passing the retirementEventId. The information provided is set in the RetirementCertificate NFT.

Note: This information is publicly written to the blockchain in plaintext.

function retireAndMintCertificate(
    string calldata retiringEntityString,
    address beneficiary,
    string calldata beneficiaryString,
    string calldata retirementMessage,
    uint256 amount
) external virtual;

Params

Name	Type	Description
retiringEntityString	string	An identifiable string for the retiring entity, e.g., their name
beneficiary	address	The address of the beneficiary of the retirement
beneficiaryString	string	An identifiable string for the beneficiary, e.g., their name
retirementMessage	string	A message to be included in the retirement certificate
amount	uint256	The amount to retire and issue an NFT certificate for

mintCertificateLegacy

This function mints a RetirementCertificate NFT based on the legacy retirement functionality. This function is used only for backwards-compatibility reasons. (In case you retired before the RetirementCertificates NFT was introduced, but still want the NFT.)

Some context: before the RetirementCertificates NFT was introduced, retirements didn't emit the Retired event. How much an address/entity had retired was stored solely in a mapping (mapping(address => uint256) public retiredAmount;).

• This is relevant for retirements performed before Block 27360444 on Polygon

• All retirements on Celo are compatible with RetirementCertificates

Going forward users should mint NFT either directly in the RetirementCertificates contract or using the retireAndMintCertificate() function above.

function mintCertificateLegacy(
    string calldata retiringEntityString,
    address beneficiary,
    string calldata beneficiaryString,
    string calldata retirementMessage
) external;

Params

Name	Type	Description
retiringEntityString	string	An identifiable string for the retiring entity, e.g., their name
beneficiary	address	The address of the beneficiary of the retirement
beneficiaryString	string	An identifiable string for the beneficiary, e.g., their name
retirementMessage	string	A message to be included in the retirement certificate